State of heterotrophic bacterioplankton of Yenisei estuary and the zone of Ob–Yenisei discharge in autumn in relation with environmental factors

In September 2011, variations of the total abundance of bacteria were studied, including, for the first time, the abundance of bacteria with intact membranes and active electron transport chains, as well as chlorophyll a concentrations and some hydrological and hydrochemical characteristics of water in Yenisei estuary and the zone of Ob–Yenisei river discharge. The study found abundant, viable, and actively functioning bacterioplankton to exist in the region. The absolute values of all microbiological characteristics were found to decrease with the distance from the freshened waters of Yenisei estuary toward the seawater of the Ob–Yenisei river discharge, while the percentage of bacteria with intact membranes and actively functioning microorganisms in bacterioplankton increased in the same direction. Positive correlations were found to exist between the values of all examined microbiological characteristics and the concentration in water of chlorophyll a, silicium, organic nitrogen, and oxygen, as well as water temperature. The same biological characteristics showed negative correlations with water salinity and phosphates. The spatial distribution of bacteria in the examined water body was supposed to be due mostly to the intensity of hydrodynamic processes, rather than the biogenic matter content of water.     

太湖北部湖区水体中浮游细菌的动态变化

2003年1月-12月对太湖北部湖区8个采样点进行了每月1次、为期一年的水体中浮游细菌数量的测定,并同步对溶解性有机碳(DOC),总氮,总磷,叶绿素a和温度进行了测定,结果表明:浮游细菌数量存在明显的季前变化和空间差异,夏秋季浮游细菌数量比冬春季高,最高值出现在夏季的7月份,平均值为7．43×106cell／ml,最低值出现在3月份,平均值为3．14×106cells／ml,最低值与最高值差异达73％;污染严重的河口区浮游细菌数量明显高于湖心区,最高值出现在河口的6#点,平均值为5.51×106cells／ml,比湖心区最低值8#点高83．2％,并呈现从河口、湾内至湖心随水体污染程度减轻而逐步递减的趋势;浮游细菌数量与温度和浮游植物量显著相关．而与水体中营养盐无关,预示着太湖水体中的营养盐已处于较高的水平,不再是浮游细菌生长的限制因素,而来源于浮游植物的有机碳可能是其生长的重要碳源．     

Lake morphometry and wind exposure may shape the plankton community structure in acidic mining lakes

Acidic mining lakes (pH <3) are specific habitats exhibiting particular chemical and biological characteristics. The species richness is low and mixotrophy and omnivory are common features of the plankton food web in such lakes. The plankton community structure of mining lakes of different morphometry and mixing type but similar chemical characteristics (Lake 130, Germany and Lake Langau, Austria) was investigated. The focus was laid on the species composition, the trophic relationship between the phago-mixotrophic flagellate Ochromonas sp. and bacteria and the formation of a deep chlorophyll maximum along a vertical pH-gradient. The shallow wind-exposed Lake 130 exhibited a higher species richness than Lake Langau. This increase in species richness was made up mainly by mero-planktic species, suggesting a strong benthic/littoral - pelagic coupling. Based on the field data from both lakes, a nonlinear, negative relation between bacteria and Ochromonas biomass was found, suggesting that at an Ochromonas biomass below 50 μg C L⁻¹, the grazing pressure on bacteria is low and with increasing Ochromonas biomass bacteria decline. Furthermore, in Lake Langau, a prominent deep chlorophyll maximum was found with chlorophyll concentrations ca. 50 times higher than in the epilimnion which was build up by the euglenophyte Lepocinclis sp. We conclude that lake morphometry, and specific abiotic characteristics such as mixing behaviour influence the community structure in these mining lakes.     

Seasonal biogeochemical and microbiological studies of small lakes in taiga zone of northwestern Russian (Arkhangelsk Province)

The results of biogeochemical and microbiological studies of three small lakes in southwestern Arkhangelsk province are presented. The lakes differ in their morphometric characteristics, thermal and oxygen regimes, and the extent of anthropogenic impact they experience. In the periods of summer and winter stratification, anaerobic water layers with higher phosphates, ammonium, and sulfide sulfur (hydrogen sulfide) are found to form in the bottom horizon of deep-water zones of the lakes. The highest concentrations of sulfide sulfur (150–210 μg dm⁻³) were recorded in the shallow Beloe Lake during winter low-water period, while in summer, sulfide concentration did not differ from those obtained in other lakes (∼10 μg dm⁻³). The abundance of sulfate-reducing bacteria in lake bottom sediments varied from 10 to 100000 cell cm⁻³, and the rate of sulfate reduction process varied from 29 to 3746 μg S dm⁻³ day⁻¹. Seasonal variations were revealed in hydrogen sulfide distribution over the water column and in the rate of sulfate reduction process in the upper horizons of bottom sediments in the examined lakes.     

南京玄武湖浮游细菌群落结构的季节变化及其与环境因子的关系

应用16S rRNA基因末端限制性片段长度多态性技术和多元统计方法,探究了南京玄武湖浮游细菌群落结构的季节性变化,并找出了浮游细菌群落组成分布的主要影响因子.结果表明,玄武湖4个季节中夏季Invsimpson指数、Shannon-Wiener指数和Pielou指数最高,而春季最低.非度量多维尺度分析结果显示浮游细菌群落结构存在着明显的季节性变化.Mantel检验、典范对应分析、变量分割分析表明影响玄武湖细菌群落结构最显著的环境因子为温度,其次为pH.营养盐浓度对玄武湖细菌群落结构的影响不显著.总的来说,本研究将有助于更好地理解富营养化水体中的浮游细菌群落组成的季节变化规律.     

How many seasons are there in a sub-tropical lake? A multivariate statistical approach to determine seasonality and its application to phytoplankton dynamics

Seasonal patterns in factors that affect primary producers are an important part of defining the structure and function of aquatic ecosystems. However, defining seasonality is often more difficult in aquatic than in terrestrial ecosystems, particularly in subtropical and tropical environments. In this study, a long-term data set for a shallow subtropical lake (Lake George, Florida, USA) was used to investigate seasonality using a range of physical, chemical and hydrological parameters. K-means cluster analysis of monthly averages among 11 selected environmental factors across 18 years suggested the overall annual pattern consists of three different seasonal clusters: a cold season (January–April), a warm season (May–August) and a flushing season (September–December). High dissolved oxygen and increased Secchi depth are key features of the cold season, while the warm season is characterized by high mean light irradiances, temperature, rainfalls, total nitrogen and phytoplankton biomass (as chlorophyll a level). The flushing season is characterized by high river discharge rates and high levels of dissolved nutrients and colored organic matter. Multiple response permutation procedures indicated that these seasonal cluster arrangements were significantly different than randomly permuted clusters (A-statistics = 0.3314, significance of delta = 0.0160, based on 1000 permutations). Results from principal component analyses supported the presence of the three seasons in the lake. Linear models explaining chlorophyll a levels using the 3-season system generally indicated better ratios of explained variance compared to the models without seasonal alignments, further indicating that even for sub-tropical systems defining seasons provides a better understanding of phytoplankton dynamics. The approaches used in this study provide statistically-based multivariate tools for the definition of seasonality in aquatic ecosystems. The ability to accurately define seasons is a key step in modeling the structure and dynamics of aquatic ecosystem, which is essential to the development of effective management strategies in a rapidly changing world.     

Distribution, abundance and life history of Mysis relicta (Lovén) in the Feldberg Lake District, Germany

Distribution, abundance and life history characteristics of Mysis relicta were studied in the Feldberg Lake District (Lake Breiter Luzin, Lake Schmaler Luzin, Lake Zansen) located in northeastern Germany. Between July 2001 and November 2002 mysids were collected by vertical net hauls. In order to determine the impact of the current trophic conditions on the distribution of mysids in these lakes, oxygen concentration, total phosphorus, chlorophyll a and water transparency were also measured. All investigated lakes are mesotrophic at present. Lake Breiter Luzin exhibited great seasonal and spatial variations in mysid abundance. Density of adults and juveniles had a mean of 44.9 ± 57.1 and 68.7 ± 99.6 m⁻², respectively. Highest abundance of adults was 110.4 ± 76.5 m⁻² in summer, lowest abundances of 2.0 ± 4.0 m⁻² occurred in spring. For juveniles, highest density of 218.4 ± 174.6 m⁻² was detected in summer and lowest of 0.8 ± 1.8 m⁻² in winter. No mysids were caught in any of the daytime hauls, but they were widely distributed throughout the water column at night. Size frequency distribution of mysids suggested that reproduction occurred year-round, the most consistent influx of juveniles occurred in early summer and a smaller second cohort in autumn. Highest mysid abundance was 189.2 ± 318.6 adults and 127.0 ± 66.3 juveniles m⁻² in Lake Schmaler Luzin, and 59.6 ± 5.6 adults and 79.4 ± 11.2 juveniles m⁻² in Lake Zansen. There were great spatial differences in abundance in both lakes.     

太湖浮游细菌种群基因多样性及其季节变化规律

为认识湖泊中浮游细菌的多样性及其变化规律,本研究采用聚合酶链式反应-变性梯度凝胶电泳(PCR-DGGE)的方法,研究了太湖梅梁湾和湖心区浮游细菌种群16S rRNA基因多样性以及种群基因组成的季节变化特征.研究结果表明,太湖浮游细菌种群具有丰富的基因多样性.浮游细菌的丰度、DGGE条带数、种群的Shannon-Wiener指数、Simpson 指数和Pielou指数均呈现显著的季节变化规律:夏季及秋季浮游细菌的丰度、基因多样性及种群的均匀度较高,而冬季和春季则较低.浮游细菌种群的基因组成随时间变化.梅梁湾浮游细菌的丰度显著高于湖心.梅梁湾与湖心浮游细菌主要建群种的基因型存在显著差异.     

Spatial and temperal patterns in bacterioplankton communities across a river-lake continuum

Bacterioplankton play critical roles in biogeochemical cycling. Although spatial and temporal variations in bacterioplankton community compositions (BCCs) within individual habitat have been reported, knowledge gaps remain for studies conducted within different habitats. In this work, we examined the seasonal and spatial variability of BCCs in Nanfei River and Lake Chaohu which had significant environmental heterogeneity using a high-throughput sequencing technique of 16S rRNA gene amplicons. The results showed that spatial variation has a more obvious impact on the BCCs than seasonal changes. The microbial diversity gradually decreased and BCCs changed obviously along water flow direction from Nanfei River to the western and estern parts of Lake Chaohu over all seasons. LEfSe analysis showed that Nanfei River had higer abundance of species belonging to the orders Rhodocyclales, Methylococcales, Campylobacterales and Flavobacteriales, samples from eastern part of Lake Chaohu were abundant in taxonomies including the order Rickettsiales, while the western part had high abundance of taxonomies belonging to the order Chroococcales. The redundancy analysis (RDA) indicated that BCCs in Nanfei River were associated with high nutrient (TP, PO₄-P, TN, NH₃-N, NO₂-N and NO₃-N) concentrations and electrical conductivity. Variance partitioning RDA analysis indicated that the combined effects of all variables may be most important affecting BCCs. This study may provide a framework for modeling the change in bacterioplankton communities through different habitats from a river to lake.     

Disturbance of meromixis in saline Lake Shira (Siberia,Russia): Possible reasons and ecosystem response

Saline Lake Shira (Southern Siberia, Russia) was meromictic through the observation period 2002–2015. During the under-ice periods of 2015 and 2016, complete mixing of the water column was recorded for the first time, and hydrogen sulphide temporarily disappeared from the water column of the lake; i.e. in those years the lake turned to holomixis. In the summer of 2015, a sharp increase in chlorophyll a, organic carbon, zooplankton, and phytoflagellates was observed in the lake, which was probably due to the release of nutrients from the monimolimnion. Purple sulfur bacteria completely disappeared from the lake after the first mixing in 2015, and did not reappear despite the restoration of meromixis in 2017. Thus, it was demonstrated that purple sulfur bacteria are sensitive to the weakening of the stratification of Lake Shira. Based on the data of the seasonal monitoring of temperature and salinity profiles over the period 2002–2017, it was presumed that the main cause of deep mixing in 2015 was the weakening of the salinity gradient due to strong wind impact and early ice retreat in the spring of 2014. In addition, it was shown that in previous years a significant contribution to the maintenance of meromixis was made by an additional influx of fresh water, which caused a rise in the lake level in the period 2002–2007. Thus, we identified a relationship between the stratification regime of the lake and the change in its level, which provides valuable information both for the forecast of water quality and for reconstruction of the Holocene climate humidity in this region of Southern Siberia from the sediment cores of Lake Shira.     

Contributions of phosphatase and microbial activity to internal phosphorus loading and their relation to lake eutrophication

Phosphatase may accelerate the process of lake eutrophication through improving phosphorus bioavailability. This mechanism was studied in three Chinese eutrophic shallow lakes (Lake Taihu, Lake Longyang and Lake Lianhua). Phosphatase activity was related to the concentration of soluble reactive phosphorus (SRP) and chlorophyll a. Stability of dissolved phosphatase in reverse micelles may be attributed to molecular size, conformation and active residues of the enzyme. At the site with Microcystis bloomed in Lake Taihu, dissolved phosphatase activity was higher and more stable in micelles, SRP concentrations were lower in interstitial water, the contents of different forms of phosphorus and the amounts of aerobic bacteria were lower while respiration efficiency was higher in sediments. Phosphobacteria, both inorganic and organic and other microorganisms were abundant in surface water but rare in sediments. Therefore, internal phosphorus may substantially flux into water column by enzymatic hydrolysis and anaerobic release, together with mobility of bacteria, thereby initiating the bloom. In short, biological mechanism may act in concert with physical and chemical factors to drive the internal phosphorus release and accelerate lake eutrophication.     

Population dynamics of autotrophic picoplankton in relation to environmental factors in a productive lake

Spatial and seasonal fluctuations in autotrophic picoplankton (APP) abundance in a eutrophic, dimictic lake (Lake Aydat, France) were measured concurrently with a variety of environmental variables. Cell number ranged from 0.03 to 2.36×10⁶ cells·ml^–1 (highest concentrations were >5-fold higher than in oligotrophic lakes) and averaged 24 ± 7% of total picoplankton abundance (APP + heterotrophic bacteria). APP abundance (1) peaked in spring simultaneously with heterotrophic flagellate and ciliate densities, (2) decreased during the nitrogen-limited and summer stratification period, and (3) increased with fall turnover. In summer-autumn, the contribution of single-cell eukaryotic (up to 66%) and colonial prokaryotic (18%) forms to total abundance peaked in the bottom waters. Multivariate regression analyses suggest that >40% variance in APP number changes may be explained by ciliate abundance (at 0–4 m depth-range), heterotrophic flagellate number and oxygen concentration (5–9 m), and ciliate carbon biomass (10–14 m). The model accounting for changes in heterotrophic bacterial abundance (5–9 m) indicates chlorophylla concentration (r ²=58%) and ciliate abundance (r ²=34%) as dominant covariates. The data presented here suggest that micrograzers control APP abundance in Lake Aydat.     

Analysis of patterns of vertical and temporal distribution of phytoplankton using multifactorial analysis: Acidic Lake Caviahue, Patagonia, Argentina

Most existing studies on the algal communities of acid lakes are based on environments that have been caused by anthropogenic disturbances. Such lakes have a different origin compared to the natural acidic lakes and could be expected to differ also in the mechanisms controlling phytoplankton and trophic status. Planktonic community in Lake Caviahue is somewhat diverse in spite of the low pH of the water. Algae have a distinctive vertical distribution: the values of phytoplankton biomass remain constant throughout the water column and at times were highest in the upper end of the hypolimnion, forming a maximum or a layer of chlorophyll a at depth. The goal of this work was to investigate the factors influencing the seasonal and vertical distribution of phytoplankton. The lake was sampled between the years 2004 and 2006. Physical, chemical and biological parameters at different depths throughout the water column were determined. The interrelationships between environmental variables at different sampling dates were analyzed using an integration of multivariate matrices, multiple factor analysis, to analyze any joint partnerships in the samples. We found that phytoplankton biomass is dominated by Keratococcus rhaphidioides. With regard to zooplankton, we found a single species of rotifers (Philodina sp.). The two arms of the lake and the depths have different behaviours showing differences in the arms' conductivity, dissolved oxygen and pH. The more superficial layers were characterized by high values of phytoplankton and zooplankton biomass, organic and inorganic carbon, dissolved oxygen and pH. The deeper layers showed high values of chlorophyll a, ammonium and phosphorus (dissolved and particulate). From the multivariate analysis the relationships of the each algal species with pH, as a possible indicator of the degree of “acidophilia”, could be extracted.     

Dynamics and sources of dissolved organic carbon during phytoplankton bloom in hypereutrophic Lake Taihu (China)

To establish the influence of phytoplankton blooms on the dynamics and sources of dissolved organic carbon (DOC) in Lake Taihu, the concentrations and stable carbon isotope values (δ¹³C) of DOC and particulate organic carbon (POC) were analyzed, along with environmental factors, including water temperature, chlorophyll a (Chl a) concentration, phytoplankton community and total bacterial abundance, from March to August 2013 at five sites in Lake Taihu. Significant differences were observed in the DOC concentrations and δ¹³C_DOC values at the sampling sites. On average, the proportion of DOC in the total organic carbon (TOC) pool ranged from 30% ± 10% to 81% ± 7%. POC was positively associated with both Chl a concentration and cyanobacteria biomass, suggesting that cyanobacteria blooms contribute to the POC pool in Lake Taihu. Depleted ¹³C in DOC relative to POC was observed in August, indicating that DOC was partially derived from POC in August. However, Chl a explained only 40% of the variation in DOC in the entirety of Lake Taihu, and at two sites far from the estuary, the contribution of allochthonous carbon was less than 50% in August. These results suggested a greater influence of allochthonous sources on the DOC pool. Moreover, the biodegradability of DOC was further determined by the total dissolved carbohydrates to DOC ratio (TCHO/DOC), specific UV absorbance (SUVA₂₅₄), and the concentrations of bioavailable DOC (BDOC). On average, 17% of the variation in DOC was attributable to the BDOC pool, and the BDOC concentration correlated positively with Chl a, cyanobacteria biomass, and total bacterial abundance, suggesting that cyanobacteria–derived DOC is biodegradable and is preferentially utilized by bacteria.     

Bacterioplankton and phytoplankton production in seven lakes in the Middle Rio Doce basin, south-east Brazil

The purpose of this study was to measure the phytoplankton production (PP) and bacterial production (BP) simultaneously in seven lakes in the middle Rio Doce basin (southeast Brazil) during the dry and the rainy seasons. Limnological monitoring was conducted from 1999 to 2001 as well as both PP (radioactive carbon fixation) and BP (³H-Leucine incorporation) in four specific depths (100%, 10%, 1% of incident radiation, and aphotic zone). Furthermore, trophic state of the lakes was analyzed, considering the index proposed by Salas and Martino (1991) and Carlson (1977). In general, some parameters increased during the rainy season such as pH, conductivity, chlorophyll and total nitrogen. In the period of 1999/2000, the rain caused PP reduction in the lakes, excepting Carioca and Águas Claras Lake, but in the years 2000/2001, the lakes did not show a similar pattern. In contrast, the rainy season of both years caused an expressive bacterioplankton production enhancing. Using Salas and Martino index, we observed that some lakes were affected by the seasonal runoff, therefore the typologie of these lakes changed from oligotrophic to mesotrophic conditions, otherwise considering the Carlson index all lakes were classified as eutrophic in both dry and rainy seasons. Indeed, Salas and Martino index demonstrated to be more appropriate to determine the trophic status of the lakes. Finally, our data indicate that until now, in spite of the lakes location, protected and unprotected area, the lakes still maintain their natural characteristics.     

Limnology of four saline lakes in western Victoria, Australia: II. Biological parameters

Major biological parameters of four permanent (Lake Colac, Modewarre, Bolac and Tooliorook), shallow and slightly saline lakes in the volcanic plains of western Victoria, Australia recorded bi-monthly between November 1999–September 2001 are described. Chlorophyll a concentration ranged from 3–29 μg l⁻¹ with peaks in autumn. Phytoplankton taxa recorded were diverse, with Chlorophyta and Bacillariophyta being common. Cyanobacterial blooms were recorded mostly in summer. Zooplankton abundance in the lakes ranged from 12–368 individuals per litre. Rotifera dominated Lake Bolac, Copepoda dominated Lake Modewarre and they co-dominated Lake Colac and Tooliorook. Zooplankton interactions with phytoplankton suggest that simple predator-prey relationships cannot fully explain the trends exhibited and that a more complex model was acting to regulate algal biomass. A decline in the abundance of zooplankton in summer in Lake Modewarre was attributed to predation by high number of exotic larval carp at that time of the year. A total of 25 benthic macroinvertebrate taxa were recorded from Lake Colac, 30 from Modewarre, 22 from Bolac and 35 from Tooliorook. Twenty-one of the 45 taxa identified occurred in at least three lakes. Nine of the 12 taxa that occurred in only one lake were from Lake Tooliorook. Simpson's diversity index was low in Lake Bolac when compared to other three lakes. Lake Modewarre had more benthic individuals (3246 Ind m⁻²) than other three lakes (range 624–1397 Ind m⁻²). The combined contribution of Ostracoda, Amphipoda and Gastropoda dominated the benthos in all the lakes throughout the study period. Macroinvertebrate taxa richness was higher in the present study lakes than recorded from the lakes in the region. Frequency of sampling and number of sampling sites seemed more important in determining species richness than the size and shallowness of the lakes.     

Impacts of meteorological variations on urban lake water quality: a sensitivity analysis for 12 urban lakes with different trophic states

Response of 12 urban lakes with different trophic states in Beijing to variations of meteorological factors was studied in this research. Monthly water quality parameters, including total nitrogen (TN), total phosphorus (TP), chlorophyll a, chemical oxygen demand (COD), biological oxygen demand (BOD), dissolved oxygen, and water temperature, were analyzed from 2009 to 2011. Results indicated that TN in the urban lakes did not exhibit significant response to meteorological variations owing to relatively lower TN concentration in the urban soil. For the highly eutrophic lakes, TP, chlorophyll a, COD, and BOD were positively correlated with precipitation, and negatively correlated with wind speed (p < 0.05). Chlorophyll a showed significant positive correlation with TP and temperature. Moreover, the abrupt increase of TP occurred in spring, which was associated with higher temperature induced internal phosphorus loading. On average, temperature/precipitation and wind speed/sunshine duration contributed to 10.7–43.8 and 8.3–19.2 % of the variations in water quality. In contrast, lakes with mesotrophication/light eutrophication did not show significant sensitivity to meteorological variations owing to their better buffer capacity and regulation effect of algae growth. Beijing is undergoing increased temperature and heavy rainfall frequency as well as decreased wind speed during the past five decades; the above results infer that water quality of most urban lakes of Beijing is becoming worse under this climate change trend. This study suggested that urban lakes with different trophic states will respond differently to global climate change, and highly eutrophic lakes might face big challenges of water quality deterioration and algae bloom.     

Validation of SeaWiFS chlorophyll a in Massachusetts Bay

Massachusetts Bay, a semi-enclosed embayment (50×100 km) in the Northwest Atlantic, is the focus of a monitoring program designed to measure the effects of relocating the Boston Harbor sewage outfall to a site 15 km offshore in Massachusetts Bay. The Massachusetts Water Resources Authority (MWRA) in situ monitoring program samples selected stations up to 17 times per year to observe seasonal changes in phytoplankton biomass and other water quality variables. We investigated the feasibility of augmenting the monitoring data with satellite ocean color data to increase the spatial and temporal resolution of quantitative phytoplankton measurements. In coastal regions such as Massachusetts Bay, ocean color remote sensing can be complicated by in-water constituents whose concentrations vary independently of phytoplankton and by inaccurate modeling of absorbing aerosols that tend to be concentrated near the coast. An evaluation of in situ and sea-viewing wide field-of-view sensor (SeaWiFS) measurements from 1998 to 2005 demonstrated that SeaWiFS overestimated chlorophyll a mainly due to atmospheric correction errors that were amplified by absorption from elevated concentrations of chlorophyll a and colored dissolved organic matter. Negative water-leaving radiances in the 412 nm band, an obvious artifact of inadequate atmospheric correction, were recorded in approximately 60–80% of the cloud-free images along the coast, while the remaining portions of the Bay only experience negative radiances 35–55% of the time with a clear nearshore to offshore decrease in frequency. Seasonally, the greatest occurrences of negative 412 nm radiances were in November and December and the lowest were recorded during the summer months. Concentrations of suspended solids in Massachusetts Bay were low compared with other coastal regions and did not have a significant impact on SeaWiFS chlorophyll a measurements. A regional empirical algorithm was developed to correct the SeaWiFS data to agree with in situ observations. Monthly SeaWiFS composites illustrated the spatial extent of a bimodal seasonal pattern, including prominent spring and fall phytoplankton blooms; and the approximate 115 cloud-free scenes per year revealed interannual variations in the timing, magnitude and duration of phytoplankton blooms. Despite known artifacts of SeaWiFS in coastal regions, this study provided a viable chlorophyll a product in Massachusetts Bay that significantly increased the spatial and temporal synoptic coverage of phytoplankton biomass, which can be used to gain a comprehensive ecosystem-wide understanding of phytoplankton dynamics at event, seasonal and interannual timescales.     

Suspended sediment,nutrients, and chlorophyll in tropical floodplain lakes with different patterns of hydrological connectivity

The ecological functioning of floodplain lakes is largely influenced by the interaction with the river mainstem. In this study, seasonal variation in water chemistry and the relationship with the river conditions were compared between floodplain lakes that differ in the level of connection to the Usumacinta River, the largest river of Mesoamerica. Samples for suspended solids, nutrients, and chlorophyll a were collected through the year in lakes permanently connected to the river and in lakes that only received water from the Usumacinta for a short period during peak flow. Floodplain lakes showed higher total suspended solids than the river during the dry season while during the rainy season greater differences were observed between the river and the lakes, probably explained by higher concentrations in the river and greater sedimentation in the lakes. Greater organic matter content in the suspended solids was observed in the floodplain lakes, particularly in the more isolated lakes, likely related to high algal biomass. Nitrate concentrations were always higher in the river than in the lakes and lower nitrate concentrations occurred at the isolated lakes, suggesting that processes that remove nitrate occur through the year and are a common feature of floodplain lakes. Phosphorus in the connected lakes was higher than in the river only during the dry season, while in the isolated lakes concentrations were always greater than in the river. Chlorophyll a concentrations were higher in the connected lakes than in the river only during the dry season, while the more isolated lakes exhibited higher values through the year, showing signs of eutrophication. Suspended organic matter, nitrate, and chlorophyll showed larger differences between lake and river sites in the more isolated lakes, probably related to greater water residence time and its influence on primary production. Less connected lakes are more vulnerable to flow alteration because the brief period of connection to the river can be compromised and the effects of eutrophication exacerbated.