Modeling the response of primary production and sedimentation to variable nitrate loading in the Mississippi River plume

Increases in nitrate loading to the Mississippi River watershed during the last 50 years are considered responsible for the increase in hypoxic zone size in Louisiana-Texas shelf bottom waters. There is currently a national mandate to decrease the size of the hypoxic zone to 5000 km² by 2015, mostly by a 30% reduction in annual nitrogen discharge into the Gulf of Mexico. We developed an ecosystem model for the Mississippi River plume to investigate the response of organic matter production and sedimentation to variable nitrate loading. The nitrogen-based model consisted of nine compartments (nitrate, ammonium, labile dissolved organic nitrogen, bacteria, small phytoplankton, diatoms, micro- and mesozooplankton, and detritus), and was developed for the spring season, when sedimentation of organic matter from plume surface waters is considered important in the development of shelf hypoxia. The model was forced by physical parameters specified along the river-ocean salinity gradient, including residence time, light attenuation by dissolved and particulate matter, mixed layer depth, and dilution. The model was developed using measurements of biological biomasses and nutrient concentrations across the salinity gradient, and model validation was performed with an independent dataset of primary production measurements for different riverine NO₃ loads. Based on simulations over the range of observed springtime NO₃ loads, small phytoplankton contributed on average 80% to primary production for intermediate to high salinities (>15), and the main contributors to modeled sedimentation at these salinities were diatom sinking, microzooplankton egestion, and small phytoplankton mortality. We investigated the impact of limiting factors on the relationship between NO₃ loading and ecosystem rates. Model results showed that primary production was primarily limited by physical dilution of NO₃, followed by abiotic light attenuation, light attenuation due to mixing, and diatom sinking. Sedimentation was mainly limited by the first three of these factors. Neither zooplankton grazing or plume residence times acted as limiting factors of ecosystem rates. Regarding nutrient reductions to the watershed, simulations showed that about half of the percent decrease in NO₃ load was reflected in decreased plume sedimentation. For example, a 30% decrease in NO₃ load resulted in a 19% decrease in average plume primary production and a 14% decrease in sedimentation. Finally, our model results indicated that the fraction of primary production exported from surface waters is highly variable with salinity (7–87%), a finding which has important implications for predictive models of hypoxic zone size that assume a constant value for this ratio.     

Inventory of nutrients in the Bohai

Biogeochemical observations were carried out to address the influence of major sources on nutrient composition and the ecosystem of the Bohai. Relatively high concentrations of nutrients off the Huanghe mouth and the shallow water areas were observed in the Bohai suggesting the effects of tidal and residual currents and anthropogenic perturbation. Sediment in the Bohai represents a source for ammonium, phosphate and dissolved silicate, while it is a sink for nitrite and nitrate. Benthic nutrient fluxes were 2-3 times higher than the riverine input with the regeneration rate of phosphate being slower relative to DIN and dissolved silicate. The release of dissolved silicate and phosphate from sediments may mitigate the decrease of dissolved silicate and phosphate due to the reduction of freshwater discharge. Compared with submarine groundwater discharge, nutrient regeneration in sediment provides similar DIN flux, 2-5 times phosphate and dissolved silicate fluxes. DIN/P molar ratios in the three mentioned sources were 155-845, indicating that phosphorus limitation for phytoplankton growth could be intensified, which likely results in changes of ecosystems of the Bohai.     

太湖北部梅梁湾水域水质因子聚类

计算了沿梁溪河河口到太湖湖心断面上１０个监测点１７个水质因子９３组数据的Ｐｅａｒｓｏｎ相关系数和Ｋｅｎｄａｌｌ秩相关系数,进而运用最小距离法进行了因子聚类,正态分布检验和聚类结果表明,采用Ｋｅｎｄａｌｌ秩相关进行了聚类为宜,结果将诸因子聚为五大类：ＴＤＮ,ＴＮ,ＣＯＮ,ＮＯ２－Ｎ,ＮＨ４－Ｎ,ＯＨ和ＣＯＤＭｎ归为一类,ＴＤＰ,ＴＰ,ＰＯ＾３＋４和ｐＨ值归为一类;ＳＳ和ＳＤ归为一类,反映了该水域环境     

Changes in the patterns of inorganic nitrogen and TN/TP ratio and the associated mechanism of biological regulation in the shallow lakes of the middle and lower reaches of the Yangtze River

The changes of NH3-N, NO3-N, NO2-N and TN/TP were studied during growth and non-growth season in 33 subtropical shallow lakes in the middle and lower reaches of the Yangtze River. There were significant positive correlations among all nutrient concentrations, and the correlations were better in growth season than in non-growth season. When TP>0.1 mgL-1, NH3-N increased sharply in non-growth season with increasing TP, and NO3-N increased in growth season but decreased in non-growth season with TP. These might be attributed to lower dissolved oxygen and low temperature in non-growth season of the hypereutrophic lakes, since nitrification is more sensitive to dissolved oxygen and temperature than antinitrification. When 0.1 mgL-1>TP>0.035 mgL-1, TN and all kinds of inorganic nitrogen were lower in growth season than in non-growth season, and phytoplank-ton might be the vital regulating factor. When TP<0.035 mgL-1, inorganic nitrogen concentrations were relatively low and NH3-N, NO2-N had significant correlations with phytoplankton, indicating that NH3-N and NO2-N might be limiting factors to phytoplankton. In addition, TN/TP went down with decline in TP concentration, and TN and inorganic nitrogen concentrations were obviously lower in growth season than in non-growth season, suggesting that decreasing nitrogen (especially NH3-N and NO3-N) was an important reason for the decreasing TN/TP in growth season. The ranges of TN/TP were closely related to trophic level in both growth and non-growth seasons, and it is apparent that in the eutrophic and hypertrophic state the TN/TP ratio was obviously lower in growth season than in non-growth season. The changes of the TN/TP ratio were closely correlated with trophic levels, and both declines of TN in the water column and TP release from the sediment were important factors for the decline of the TN/TP ratio in growth season.     

A retrospective analysis of trace metals, C, N and diatom remnants in sediments from the Mississippi River delta shelf

The development of oil and gas recovery offshore of the Mississippi River delta began in shallow water in the 1950s, expanded into deeper waters, and peaked in the 1990s. This area of the outer continental shelf (OCS) is the historical and present location of >90% of all US OCS oil and gas production and reserves. The juxtaposition of its 4000 producing platforms, recovering $10 billion yr(-1) of oil, gas and produced water in the same area where about 28% of the US fisheries catch (by weight) is made and near 40% of the US coastal wetlands, makes this an area worth monitoring for regional pollutant loading. This loading may come from several sources, including sources related to OCS development, but also from the Mississippi River watershed. In this context, any contaminant loading on this shelf may be neither detectable nor significant against a background of climatic or biological variability. We examined the sedimentary record for indicators of industrial byproducts from OCS oil and gas development and of industrial products entering via the Mississippi River, primarily using vanadium (V) and barium (Ba) concentrations normalized for aluminum (Al). Barium is primarily used in drilling muds in the form of barite, whereas V is an important strengthening component of metal alloys, including steel. The fluctuations in the accumulation of Ba, but not V, were coincidental with the presumed use of barite. The fluctuations in V concentration in the sediments were coincidental with the national consumption of V. Copper (Cu), cadmium (Cd) and zinc (Zn) concentrations in sediments fluctuate coincidentally with V, not Ba, thus indicating that the dominant source of these trace metals in offshore sediments were derived from riverine sources, and were not primarily from in situ industrial processes releasing them on the shelf. This is not to suggest that local site-specific contamination is not a significant management or health concern. The low oxygen (hypoxia; < or = 2 mg l(-1)) zone that consistently covers much of this continental shelf's bottom layer in summer is attributed to nitrate loading from the Mississippi River. Increased nitrogen loading from river to shelf stimulates diatom production whose loading to the bottom layer and subsequent metabolism results in oxygen being depleted faster than it is replaced. In the last two decades there has been an increased accumulation of organic matter in sediments near the mouth of the Mississippi River. This coupling between river water, surface water and bottom water has recently expanded westward of the Atchafalaya River delta towards the Texas coast. The accumulation of biogenic silica (BSi) and carbon in dated sediments is coincidental with variations in riverine nitrate flux, but not with either V or Ba accumulation rates. These analyses indicate that both OCS development and riverine sources exert strong influences on the sediment constituents offshore, and that these influences may be independent of one another.     

夏季滇池和入滇河流氮、磷污染特征

为探讨滇池入湖河流水体营养盐空间分布特征及其对滇池水体富营养化的影响,2014年7月采集了入滇4类典型河流(城市纳污型河流、城乡结合型河流、农田型河流、村镇型河流)及滇池水样,分析其氮、磷浓度.结果表明:4条入湖河流总氮(TN)、总磷(TP)、硝态氮和氨氮污染均较严重;河流水体中TN、TP平均浓度大小为:农田型河流(大河)村镇型河流(柴河)城乡结合型河流(宝象河)城市纳污型河流(盘龙江),其中农田型河流(大河)水体TN、TP污染最为严重;在夏季,4条入湖河流水体中TN、TP浓度从上游向下游增加趋势比较明显,表明氮、磷沿河流不断富集;氮磷比分析表明,夏季河流输入氮、磷营养盐有利于藻类的生长,并且滇池浮游植物生长主要受TN浓度限制;夏季滇池南部入湖河流水体的TN、TP浓度高于北部入湖河流,该特征与滇池水体中TN、TP污染分布状况相反,推测滇池北部富营养化的主要影响因素是内源释放.因此,在今后的滇池水体富营养化研究中,应对滇池内源释放进行深入研究.     

The composition of nutrient fluxes from contrasting UK river basins

Accurate estimates of N and P loads were obtained for four contrasting UK river basins over a complete annual cycle. The fractionation of these loads into dissolved and particulate, and inorganic and organic components allowed a detailed examination of the nutrient load composition and of the factors influencing both the relative and absolute magnitude of these components. The particulate phosphorus (TPP) loads account for 26–75% of the annual total phosphorus (TP) transport and are predominantly inorganic. The inorganic (PIP) and organic (POP) fractions of the TPP loads represent 20–47% and 6–28% of the annual TP transport, respectively. In contrast, the particulate nitrogen loads (TPN) represent 8% or less of the annual total nitrogen (TN) loads and are predominately organic. For dissolved P transport, the dissolved inorganic fraction (DIP) is more important, representing 15–70% of the TP loads, whereas the dissolved organic fraction (DOP) represents only 3–9% of the TP loads. The TN loads are dominated by the dissolved component and more particularly the total oxidized fraction (TON), which is composed of nitrate and nitrite and represents 76–82% of the annual TN transport. The remaining dissolved N species, ammonium (NH₄-N) and organic N (DON) account for 0·3–1·2% and 13–16% of the annual TN transport, respectively. The TPN and TPP fluxes closely reflect the suspended sediment dynamics of the study basins, which are in turn controlled by basin size and morphology. The dissolved inorganic nutrient fluxes are influenced by point source inputs to the study basins, especially for P, although the TON flux is primarily influenced by diffuse source contributions and the hydrological connectivity between the river and its catchment area. The dissolved organic fractions are closely related to the dissolved organic carbon (DOC) dynamics, which are in turn influenced by land use and basin size. The magnitude of the NH₄-N fraction was dependent on the proximity of the monitoring station to point source discharges, because of rapid nitrification within the water column. However, during storm events, desorption from suspended sediment may be temporarily important. Both the magnitude and relative contribution of the different nutrient fractions exhibit significant seasonal variability in response to the hydrological regime, sediment mobilization, the degree of dilution of point source inputs and biological processes. © 1998 John Wiley & Sons, Ltd.     

Effects of nitrogen and phosphorus on phytoplankton composition and biomass in 15 subtropical, urban shallow lakes in Wuhan, China

This study aims at investigating the composition and biomass of the phytoplankton community in 15 urban shallow eutrophic lakes as well as the effects of main environmental factors, including nutrient concentrations and the ratio of nitrogen to phosphorus, temperature, COD, BOD, water depth, etc. on the phytoplankton community structure. Lake water samples were taken and analyzed on a bimonthly basis during the period from March 2004 to March 2006. The redundancy analysis (RDA) and regression analysis (RA) were performed to identify the effects of nutrients on the phytoplankton community and biomass in these typical urban lakes. The results indicate that most of these urban lakes were hypertrophic due to high concentrations of total phosphorus (TP) and total nitrogen (TN), with mean levels of 490 and 5380 mg m⁻³, respectively. The phytoplankton community was dominated by Microcystis aeruginosa and Euglena caudate in summer and Cryptomonas ovata and Cyclotella meneghiniana in winter. The mean biomass of the phytoplankton reached 456.87 mg L⁻¹ in summer months and the annual level was 189.24 mg L⁻¹. Temperature and TP content were found to be the principal limiting factors for phytoplankton growth on an annual basis. On the other hand, the results of RDA and RA demonstrate that the dominant phytoplankton species were not nutrient-limited during summer months. Low TN:TP ratios (<10) were detected accompanied with fewer occurrences of N-fixing cyanobacteria and other filamentous algae in most lakes in summer, which implies that low N:P ratio does not always shifts the dominance of phytoplankton community to the N-fixing cyanobacteria. Moreover, TP always had higher correlation with chlorophyll a (Chl-a) than TN, even when the TN:TP ratios of most samples were lower than 10. Therefore, it is concluded that the TN:TP ratio is not always a suitable index to determine whether nitrogen or phosphorus limits the phytoplankton biomass in urban shallow eutrophic lakes.     

气候变暖和营养水平对洱海浮游植物的长期影响(1980-2009年)

气候变暖下湖泊富营养化进程是近年研究热点之一.本文对1980-2009年期间洱海富营养化进程研究发现,水体总磷、总氮与气温均呈升高趋势.气温、水体总磷和总氮均能显著促进浮游植物增长.统计分析表明,气温对浮游植物增长的促进作用不受水体总氮、总磷的影响;水体总磷对浮游植物增长的促进作用不受气温的影响,受水体总氮的影响;水体总氮对浮游植物增长的促进作用不受气温和水体总磷的单独影响,受它们共同的影响.因此,气候变暖与营养水平的增加共同促进了洱海的富营养化进程.     

2005-2017年北部太湖水体叶绿素a和营养盐变化及影响因素

利用国家生态观测网络太湖湖泊生态系统研究站对北部太湖14个监测点2005-2017年的营养盐和叶绿素a浓度逐月监测数据,分析了北部太湖2005年以来水体营养盐和叶绿素a变化特征,探讨了叶绿素变化的影响因素.结果表明,2015年以来,北部太湖水体叶绿素a浓度呈现显著增高特征,特别是5-7月的蓝藻水华灾害关键期,水体叶绿素a浓度增幅更加明显;营养盐方面,氮、磷对治理的响应完全不同：水体总氮、溶解性总氮、氨氮的降幅很明显,甚至在春末夏初的蓝藻生长旺盛期出现了供给不足的征兆;但水体总磷降幅却不明显,加之蓝藻水华的磷"泵吸作用",近3 a来水体总磷浓度反而有升高趋势,溶解性总磷浓度也无明显下降趋势.不同湖区的营养盐变化也不相同：西北湖区溶解性总氮、溶解性总磷浓度显著高于梅梁湾、贡湖湾和湖心区,而且后3个湖区的水质呈现均一化趋势.统计分析表明,北部太湖水体叶绿素a浓度与颗粒氮、颗粒磷、总磷、高锰酸盐指数均呈显著正相关,与溶解态氮呈负相关;5-7月水华关键期北部太湖水体叶绿素a浓度与上半年（1-6月）逐日水温积温、总降雨量、年平均水位均呈显著正相关关系.从研究结果可以看出,近年来北部太湖水体叶绿素a浓度的波动很大程度上受水文气象因子的影响;2007年以来太湖流域一系列生态修复工程的实施,虽然明显降低了湖泊氮浓度,但由于流域和湖体的氮磷本底较高,磷的缓冲能力大,致使水体营养盐水平仍未降到能显著抑制蓝藻生长的水平,年际之间的水文气象条件差异成为蓝藻水华暴发强度差异的主控因素.为此,仍需加大对太湖流域氮、磷负荷的削减,使湖体氮、磷浓度降低到能显著影响蓝藻生长的水平,才能摆脱水文气象条件对蓝藻水华情势的决定作用.     

太湖西部环湖河道污染物输移速率变化特征

阐明污染物出入湖输移速率对于湖泊陆域污染控制具有重要意义.本文研究了太湖西部主要环湖河道总氮（TN）、溶解性总氮（DTN）、总磷（TP）、溶解性总磷（DTP）和高锰酸盐指数（COD_Mn）输移速率变化特征.结果表明环湖河道上述指标净输入速率分别为707.9、727.0、28.8、18.2和700.9 g/s.城东港、百渎港、大浦港和沙塘港4条河道TN、DTN、TP、DTP和COD_Mn输入速率分别占西部河道总输入速率的62.7%、63.6%、67.1%、66.6%和64.8%.太浦河、长兜港和大钱港TN、DTN、TP、DTP和COD_Mn输出速率占总输出的86.5%、86.9%、85.0%、85.3%和80.6%.污染物净输入速率受水情影响,TN和DTN浓度汛前最大,而TP、DTP、COD_Mn浓度汛期增大,汛后分别降低44.2%、48.8%和39.8%.城东港氮、磷输入速率受浓度控制,其他河道各指标输移速率受流量控制.近岸湖体TN浓度与入湖速率呈显著正相关,而离岸湖体TN、TP、COD_Mn浓度对入湖速率的变化响应不明显.     

Spatial patterning of water quality in Biscayne Bay, Florida as a function of land use and water management

An objective classification analysis was performed on a water quality data set from 25 sites collected monthly during 1994-2003. The water quality parameters measured included: TN, TON, DIN, NH4+, NO3-, NO2-, TP, SRP, TN:TP ratio, TOC, DO, CHL A, turbidity, salinity and temperature. Based on this spatial analysis, Biscayne Bay was divided into five zones having similar water quality characteristics. A robust nutrient gradient, driven mostly by dissolved inorganic nitrogen, from alongshore to offshore in the main Bay, was a large determinant in the spatial clustering. Two of these zones (Alongshore and Inshore) were heavily influenced by freshwater input from four canals which drain the South Dade agricultural area, Black Point Landfill, and sewage treatment plant. The North Bay zone, with high turbidity, phytoplankton biomass, total phosphorus, and low DO, was affected by runoff from five canals, the Munisport Landfill, and the urban landscape. The South Bay zone, an embayment surrounded by mangrove wetlands with little urban development, was high in dissolved organic constituents but low in inorganic nutrients. The Main Bay was the area most influenced by water exchange with the Atlantic Ocean and showed the lowest nutrient concentrations. The water quality in Biscayne Bay is therefore highly dependent of the land use and influence from the watershed.     

Changes in the patterns of inorganic nitrogen and TN/TP ratio and the associated mechanism of biological regulation in the shallow lakes of the middle and lower reaches of the Yangtze River

The changes of NH₃-N, NO₃-N, NO₂-N and TN/TP were studied during growth and non-growth season in 33 subtropical shallow lakes in the middle and lower reaches of the Yangtze River. There were significant positive correlations among all nutrient concentrations, and the correlations were better in growth season than in non-growth season. When TP>0.1 mgL^?1, NH₃-N increased sharply in non-growth season with increasing TP, and NO₃-N increased in growth season but decreased in non-growth season with TP. These might be attributed to lower dissolved oxygen and low temperature in non-growth season of the hypereutrophic lakes, since nitrification is more sensitive to dissolved oxygen and temperature than antinitrification. When 0.1 mgL^?1>TP>0.035 mgL^?1, TN and all kinds of inorganic nitrogen were lower in growth season than in non-growth season, and phytoplankton might be the vital regulating factor. When TP<0.035 mgL^?1, inorganic nitrogen concentrations were relatively low and NH₃-N, NO₂-N had significant correlations with phytoplankton, indicating that NH₃-N and NO₂-N might be limiting factors to phytoplankton. In addition, TN/TP went down with decline in TP concentration, and TN and inorganic nitrogen concentrations were obviously lower in growth season than in non-growth season, suggesting that decreasing nitrogen (especially NH₃-N and NO₃-N) was an important reason for the decreasing TN/TP in growth season. The ranges of TN/TP were closely related to trophic level in both growth and non-growth seasons, and it is apparent that in the eutrophic and hypertrophic state the TN/TP ratio was obviously lower in growth season than in non-growth season. The changes of the TN/TP ratio were closely correlated with trophic levels, and both declines of TN in the water column and TP release from the sediment were important factors for the decline of the TN/TP ratio in growth season.     

太湖西北湖区浮游植物和无机、有机氮的时空分布特征

以太湖重度蓝藻水华发生的西北湖区为研究对象,从河口至湖心区设置5个采样点,于2012年10月至2013年10月逐月采集表层水体样品,测定了水温、溶解氧和浮游细菌丰度,并分析了浮游植物群落结构的组成、溶解性无机氮(DIN)和有机氮(DON)浓度以及氮磷比.研究结果表明,太湖西北湖区浮游植物主要由蓝藻、硅藻、绿藻和隐藻组成.可能由于风、浪等混合作用使太湖西北湖区不同采样点之间蓝藻细胞密度没有显著差异.蓝藻生物量在浮游植物中所占比例最高为34%±15%,春季部分点位隐藻生物量高于50%,表明隐藻与蓝藻的相互竞争趋势显著.CCA排序图结果表明,DIN、DON浓度以及总氮∶总磷比(TN∶TP比)是影响西北湖区浮游植物优势属分布的重要环境因子.5个采样点铵态氮(NH_4~+-N)与DIN浓度具有显著差异,与DON浓度没有显著差异.夏季蓝藻水华暴发期间,可能由于蓝藻的吸收利用引起NH_4~+-N和硝态氮(NO_3~--N)浓度迅速降低.此外,由于NH_4~+-N浓度还可能受到沉积物NH_4~+-N释放的影响,因此,蓝藻细胞密度与NO_3~--N的相关系数和显著水平均高于NH_4~+-N.夏季TN∶TP比和DIN∶TP比降至最低,表明该湖区浮游植物,尤其是蓝藻的生长可能受到氮限制.蓝藻细胞密度与DON浓度呈显著负相关,表明在氮限制条件下,DON可能是蓝藻氮素利用的重要补充.     

亚热带地区典型水库流域氮、磷湿沉降及入湖贡献率估算

为了探究汤浦水库流域氮、磷湿沉降对水库水体营养的贡献率,本研究对2014 2015年的汤浦水库流域4个采样点的雨水及3条溪流进行样品收集,测定其中磷和不同形态氮的质量浓度,分析汤浦水库流域大气湿沉降中氮、磷营养盐的分布特征,并估算氮、磷营养盐湿沉降对汤浦水库入库负荷的贡献率.结果表明:湿沉降中总氮(TN)平均浓度为1.02±0.58 mg/L,氨氮、硝态氮和有机氮浓度占TN浓度的比例分别为60.65%、34.07%和5.28%;总磷(TP)平均浓度为0.033±0.028 mg/L.4个采样点湿沉降中氮、磷浓度均表现为冬春季(少雨季)高、夏秋季(多雨季)低.空间上,王化点位的各形态氮和总磷浓度显著高于其他3个采样点.TN和TP年均湿沉降通量约为18.15和0.62 kg/(hm~2·a),年均沉降总量为834.94和28.39 t;库区TN和TP水面湿沉降量为24.14和0.82 t,直接贡献率占河流输入的1.77%和3.07%.湿沉降来源的氮、磷营养盐随河流输入的间接贡献率为8.3%和4.6%.综上所述,氮、磷湿沉降是水库外源营养的重要输入部分,深入掌握其时空分布特征及入库贡献率是进一步加强流域管理和减轻水库外源营养输入的重要前提.     

夏季短期调水对太湖贡湖湾湖区水质及藻类的影响

贡湖湾作为"引江济太"工程长江来水进入太湖的第一站,湖湾水体生态环境的变化是对调水工程净水效果的最好响应,因此本文针对贡湖湾一次夏季短期调水展开调查研究,分别取2013年7月24日(调水前)和2013年8月18日(短期调水后)两次监测水样的水体理化指标和浮游藻类群落数据进行了对比分析,并对浮游藻类群落与环境因子做了相关性分析.结果表明:受来水影响,短期调水后监测区水体的p H略有下降,溶解氧、浊度、硝态氮、总氮、总磷以及高锰酸盐指数等水体理化指标浓度均较调水前有所升高;其中受调水影响最为显著的区域为望虞河的入湖口区、湾心区.两次监测调水前后湖区水体优势藻种属未发生变化,仍以微囊藻为主,但蓝藻种属比例有所下降,绿藻和硅藻等种属比例则有所上升.望虞河入湖口区和贡湖湾湾心区的Shannon-Wiener多样性指数和Pielou均匀度指数受调水的影响升高.同时,浮游藻类群落结构与受水水体理化参数的冗余分析结果表明,此次监测的短期调水后,太湖贡湖湾监测湖区水体p H、溶解氧、硝态氮、总氮、总磷、高锰酸盐指数等环境因子与浮游藻类的群落分布呈显著相关,是影响受水水体中藻类群落的主要环境因子.     

Predicting summer hypoxia in the northern Gulf of Mexico: redux

We report on the evolution and accuracy of a model used to predict the mid-summer area of hypoxia (oxygen ≤2 mg l(-1)) in the northern Gulf of Mexico, use it to test for impacts from the Deepwater Horizon oil spill (2010), and estimate the N loading that would meet a management goal. The prediction since 2000 were 100%±6% (μ±1 SE) of the actual value. The predicted in 2010 was 99% of that actual value, suggesting that the net effect of the 2010 oil spill on the hypoxic zone size was negligible. A tropical storm, however, may have reduced the potential size of the hypoxic zone. Lowering the May nitrogen load to about 70,000 mton N nitrate+nitrite would bring the model's predicted hypoxic zone size down to the management goal of 5000 km(2) and restore hypoxic waters to normoxic conditions.     

洪泽湖出入河流及湖体氮、磷浓度时空变化(2010—2019年)

基于2010-2019年洪泽湖湖体水质逐月监测数据,筛选出影响湖体水质的主要污染物指标为总氮（TN）和总磷（TP）;选取洪泽湖周边25条主要入湖河流和2条出湖河流在2019年10月2020年9月的监测数据,探讨河流外源性输入对不同湖体区域氮磷的影响及其水期变化规律.结果发现：①湖体TN、TP浓度长期居高不下,年均浓度范围分别在1.39~1.86、0.080~0.171 mg/L波动.主要入湖河流TN、TP时空平均浓度（1.92~5.70和0.114~0.181 mg/L）,均高于同区域湖体（1.15~1.46和0.088~0.101 mg/L）,其中北部入湖河流肖河、马化河和五河与临近湖区TN、TP浓度呈现显著正相关,是影响北部湖体TN、TP浓度的主要河流;南部入湖河流维桥河和高桥河是临近湖区非极端降雨期TN、TP的主要来源.②调水工程对湖体及入湖河流TN、TP浓度分布影响显著,调水期湖体沿调水方向TP浓度逐渐上升,TN浓度则呈现先降后升的趋势,南部入湖河流维桥河和高桥河TN浓度达到水期峰值,分别为10.69和9.90 mg/L.③极端降雨期入湖河流的TN、TP浓度显著高于其它水期,由于湖体对TN、TP的富集作用不同,TP浓度呈现中间高,四周低,而TN浓度呈现沿洪水流向逐渐降低的规律.     

2007-2008年千岛湖营养盐时空分布及其影响因素

2007-2008年对千岛湖水体中5个采样点(S1,S3,S4,S8,S9)的总氮、总磷、三态氮、溶解性总磷和可溶性活性磷等进行了不同深度的逐月监测,以研究探讨千岛湖营养盐的时空分布格局.结果表明,两年间总磷、总氮和硝酸盐氮浓度都呈现从上游(S1)至下游(S9)逐渐下降的趋势;2007-2008年汛期(3-7月)位于千岛湖上游新安江干流段的样点S1各种营养盐均为全年最高.但是2007年与2008年营养盐时空分布差异显著.2008年汛期(3-7月),S1的总磷和总氮浓度分别极显著低于和高于2007年同期.相对于2007年,虽然2008年具有更高的温度,但没有增强水体热稳定性.2008年强对流天气一方面通过打破水体热分层和促进水体混合,另一方面通过雨水带来大量的地表营养盐来影响营养盐的分布.汛期高浓度的总磷在1-2个月内平均降低64.4%,最大降低88.6%,显示千岛湖生态系统具有较强的净化能力.分析结果显示千岛湖营养盐时空分布总体格局是由水文、生物以及人类活动等各种因素之间的相互作用所产生的综合效应而形成的,而极端天气能够改变这一格局.     

东巢湖湖滨农田生态拦截沟中浮游植物群落结构

在巢湖市烔炀镇西宋村农田示范基地中建立生态拦截沟来处理农业生产排放的农业面源污水,就生态拦截沟中浮游植物丰度、生物量和群落结构进行了研究.实验历时6个月,研究中共检测到浮游植物9门48属75种.研究发现尽管农田生态拦截沟中的水生植被能有效削减水体中的氮、磷营养盐,但对浮游植物群落结构产生的影响不大.生态拦截沟中主要藻类为绿藻、蓝藻和硅藻,且出水口蓝藻所占比例较进水口有显著上升.生态拦截前后浮游植物优势种类的变化不大,主要为蓝藻门的铜绿微囊藻(Microcystis aeruginosa)、绿藻门的微球衣藻(Chlamydomonas microsphaera)和硅藻门的孟氏小环藻(Cyclotell meneghiniana)等.藻类生物多样性研究表明生态拦截沟中的水体主要为清洁或寡污型水体,仅在夏季的7月份出现了轻微的水体污染.典型对应分析发现,TN/TP对浮游植物种类分布的解释度最高.同时,发现水体总磷的对数、总溶解磷的对数与藻类的生物量呈正比,而TN/TP与藻类的生物量呈反比.研究表明农田生态拦截沟尽管具有削减农业氮、磷营养盐面源污染的作用,但不能有效地降低水体中蓝藻的生物量.农业面源污水中的藻类营养盐限制主要为磷限制,削减农田径流中的磷含量是控制巢湖流域水体富营养化和遏制蓝藻水华的关键环节.