Plankton and dissolved inorganic carbon isotopic composition in a river-dominated estuary: Apalachicola Bay, Florida

To characterize the isotopic composition of organisms at the base of the food web and the controls on their variability, the concentration and δ¹³C isotopic composition of dissolved inorganic carbon (DIC) and plankton δ¹³C, δ¹⁵N, and δ³⁴S were measured. The measurements were made during periods of high and low river flow in Apalachicola Bay, Florida, United States, over 3 yr. DIC concentration and δ¹³C values were related to salinity, indicating that conservative mixing of riverine and marine waters was responsible for the overall distributions. The usefulness of DIC δ^13C data for characterizing the trophic processes within the estuary was dependent upon the residence time of water within the season. Plankton δ¹³C values varied from −22‰ to −30‰ and were directly related to estuarine DIC δ¹³C, offset by a factor of roughly −20‰. This offset factor varied with salinity. Values of δ³⁴S in estuarine plankton (station means ranged from 11.4‰ to 13.1‰) were depleted relative to marine plankton (17.7±0.4‰) possibly due to the admixture of³⁴S-depleted sedimentary sulfide with estuarine samples. Values of δ³⁴S in plankton were not related to δ¹³C values of plankton and were only weakly correlated to the salinity of the water from which the plankton were collected, indicating that marine sulfate was the primary source of planktonic sulfur. Values of δ¹⁵N in plankton varied from 5.5‰ to 10.7‰ and appeared related to dominance of the sample by phytoplankton or zooplankton. Estuarine plankton was¹⁵N enriched relative to offshore plankton and estuarine sediment.     

Variation and uncertainty in evaporation from a subtropical estuary: Florida Bay

Variation and uncertainty in estimated evaporation was determined over time and between two locations in Florida Bay, a subtropical estuary. Meteorological data were collected from September 2001 to August 2002 at Rabbit Key and Butternut Key within the Bay. Evaporation was estimated using both vapor flux and energy budget methods. The results were placed into a long-term context using 33 years of temperature and rainfall data collected in south Florida. Evaporation also was estimated from this long-term data using an empirical formula relating evaporation to clear sky solar radiation and air temperature. Evaporation estimates for the 12-mo period ranged from 144 to 175 cm yr⁻¹, depending on location and method, with an average of 163 cm yr⁻¹ (±9%). Monthly values ranged from 9.2 to 18.5 cm, with the highest value observed in May, corresponding with the maximum in measured net radiation. Uncertainty estimates derived from measurement errors in the data were as much as 10%, and were large enough to obscure differences in evaporation between the two sites. Differences among all estimates for any month indicate the overall uncertainty in monthly evaporation, and ranged from 9% to 26%. Over a 33-yr period (1970–2002), estimated annual evaporation from Florida Bay ranged from 148 to 181 cm yr⁻¹, with an average of 166 cm yr⁻¹. Rainfall was consistently lower in Florida Bay than evaporation, with a long-term average of 106 cm yr⁻¹. Rainfall considered alone was uncorrelated with evaporation at both monthly and annual time scales; when the seasonal variation in clear sky radiation was also taken into account both net radiation and evaporation were significantly suppressed in months with high rainfall.     

Lithium isotopes in foraminifera shells as a novel proxy for the ocean dissolved inorganic carbon (DIC)

Past ocean pH and pCO₂ are critical parameters for establishing relationships between Earth's climate and the carbon cycle. Previous pCO₂ estimates are associated with large uncertainties and are debated. In this study, laboratory cultures of the foraminiferan genus Amphistegina were performed in order to examine the possible factors that control the Li isotope composition (δ⁷Li) of their shells. δ⁷Li is insensitive to temperature and pH variations but correlates positively with the Dissolved Inorganic Carbon (DIC) of seawater. Li/Ca ratio in the shells shows negative correlation with δ⁷Li, consistent with published data for planktonic foraminifera from core tops and from short periods during the Cenozoic. We propose that the sensitivity of δ⁷Li and Li/Ca ratio to DIC is a biological phenomenon and is related to biomineralization mechanisms in foraminifera. We used the published foraminiferal δ⁷Li records, and our experimental results, to determine the paleo-ocean DIC and pH for the last glacial–interglacial cycle. The results are consistent with published estimates of pH and pCO₂ based on boron isotopes and ice cores. We suggest Li and its isotopes may serve as a new complementary proxy for the paleo-ocean carbonate chemistry.     

重庆地区岩溶地下河水溶解无机碳及其稳定同位素特征

稳定碳同位素是指示岩溶动力系统碳来源及转化的重要指标。为揭示重庆地区岩溶地下水中溶解无机碳基本特征和碳来源,本文对该地区63条岩溶地下河水样进行了水化学和碳同位素分析。研究结果表明,重庆地区地下河水溶解无机碳主要表现形式为HCO3-,雨季由于稀释作用其浓度低于旱季。重庆岩溶地下河水δ13C-DIC（V-PDB）旱季变化范围为-15.34 ‰～-5.89 ‰,雨季变化范围为-17.40 ‰～-4.23 ‰。根据δ13C同位素质量平衡方法,计算得到重庆地下河旱季碳酸盐岩溶蚀对DIC贡献为45.1 % ～79.7 %,雨季平均为34.6 %～82.1 % 。计算结果表明,在人类活动不断增强的情况下,岩溶水体DIC通量中碳酸盐岩溶解来源的DIC和其参与岩溶地下水δ13C值的形成并不一定是岩溶作用理论方程中所计算的50 %,而是有一定的变化范围。因此在计算岩溶作用碳汇时,建议通过δ13C值扣除碳酸盐岩溶蚀形成DIC的通量后再来推算岩溶作用形成的碳汇量。     

Radiocarbon dating of dissolved inorganic carbon in groundwater from confined parts of the Upper Floridan aquifer, Florida, USA

Geochemical reaction models were evaluated to improve radiocarbon dating of dissolved inorganic carbon (DIC) in groundwater from confined parts of the Upper Floridan aquifer in central and northeastern Florida, USA. The predominant geochemical reactions affecting the ¹⁴C activity of DIC include (1) dissolution of dolomite and anhydrite with calcite precipitation (dedolomitization), (2) sulfate reduction accompanying microbial degradation of organic carbon, (3) recrystallization of calcite (isotopic exchange), and (4) mixing of fresh water with as much as 7% saline water in some coastal areas. The calculated cumulative net mineral transfers are negligibly small in upgradient parts of the aquifer and increase significantly in downgradient parts of the aquifer, reflecting, at least in part, upward leakage from the Lower Floridan aquifer and circulation that contacted middle confining units in the Floridan aquifer system. The adjusted radiocarbon ages are independent of flow path and represent travel times of water from the recharge area to the sample point in the aquifer. Downgradient from Polk City (adjusted age 1.7 ka) and Keystone Heights (adjusted age 0.4 ka), 14 of the 22 waters have adjusted ¹⁴C ages of 20–30 ka, indicating that most of the fresh-water resource in the Upper Floridan aquifer today was recharged during the last glacial period. All of the paleowaters are enriched in ¹⁸O and ²H relative to modern infiltration, with maximum enrichment in δ¹⁸O of approximately 2.0‰. Electronic Publication     

Phytoplankton biomass in a subtropical estuary: Distribution,size composition,and carbon:Chlorophyll ratios

The seasonal pattern of phytoplankton biomass (chlorophyll and particulate organic carbon) and the salinity-related pattern of phytoplankton biomass and size composition were determined in Apalachicola Bay, Florida, throughout 2004. Phytoplankton biomass was highest during summer and lowest during winter. During summer, phytoplankton biomass was highest in waters with salinity between about 5 and 23. In waters between 5 and 23, phytoplankton biomass was primarily (> 50%) composed of < 5 μm cells. The results from this study support the idea that a microbial food web characterizes mass and energy flow through the planktonic food web in Apalachicola Bay and other estuaries. During winter, the carbonxhlorophylla ratio averaged 56 ± 60 (standard deviation). During summer, the ratio ranged from 23 to 345, with highest values occurring in waters with salinity between about 8 and 22. The carbonxhlorophylla ratio was positively related to the percent of chlorophyll < 5 μm in size during summer.     

Stable isotope analysis of carbon cycling in the Perdido estuary, Florida

Stable carbon isotope (δ¹³C) analysis was used in the Peridido Estuary, Florida U.S. to determine the predominant carbon source that supports the bacterial assemblage. Stable carbon isotope values were measured in the suspended particulate matter (SPM), dissolved organic and inorganic matter, and bacteria. Stable nitrogen isotope (δ¹⁵N) ratios were measured in SPM and nitrate to assist in understanding carbon cycling through the estuary. Analyses were conducted on samples from riverine, coastal, and anthropogenic sources and compared with samples from the bay. Stable isotope ratio analysis was coupled with estimates of mixing of riverine and coastal waters into the bay. Preliminary observation of the °¹³C data indicates that terrestrial organic matter is the primary carbon source that is assimilated by bacteria in the ecosystem. Stable isotope data from carbon and nitrogen pools in combination with analysis of estuarine current velocities indicates that primary production is an important factor in the carbon cycle. This study demonstrates the importance of stable isotope analysis of multiple carbon and nitrogen pols to assess sources and cycling of organic matter.     

连续流同位素质谱测定水中溶解无机碳含量和碳同位素组成的方法研究

用连续流同位素质谱对水样中溶解无机碳含量和碳同位素组成的测量方法进行了研究,使用德国Finnigan公司DeltaPlusXP同位素质谱仪和GasBenchⅡ在线制样装置对实验室制备的四个实验室标准进行了反应流程、平衡时间、信号强度、数据精度、标准稳定性等检测,结果显示平衡时间大于4h检测信号达到稳定,同时发现44CO2信号强度和水样中溶解无机碳(DIC)浓度具有很好的相关性,因此可以利用信号强度来计算原样品中的DIC浓度。在四个实验室标准中,由NaHCO3配置的标准具有非常好的稳定性和精度,可以作为测试的工作标准。本方法测量水样中溶解无机碳的δ13C分析精度为0.1‰。本方法可以广泛应用于自然界各种水体中溶解无机碳(DIC)含量及其稳定碳同位素组成的分析。     

Using stable isotope analyses to assess carbon dynamics in a shallow subtropical estuary

The sources of carbon, which fuel water column respiration, remain unresolved for most estuaries; our objective was to examine carbon dynamics in a shallow subtropical estuary. We sampled the Sabine-Neches estuary, Texas, during low (November 1999) and high (May 2000) freshwater inflow and measured stable carbon isotope ratios of the dissolved inorganic and orgnaic carbon (δ¹³C-DIC, δ¹³C-DOC), as well as quantifying accessory parameters (salinity, nutrients, total suspended solids, and photosynthetic pigments). Pigment analysis indicated that diatoms were the predominant phytoplankton. Data from the May 2000 sampling event exhibited conservative mixing, indicating that the system was acting as a conduit between the watershed and the Gulf of Mexico. During November, mixing was generally nonconservative indicating extensive recycling of allochthonous and autochthonous carbon sources. Our data imply that both carbon sources had similar isotope, ratios that made it impossible to unambiguously determine the dominant source supporting respiration. The nonconservative DIC concentration data indicating an autotrophic sink as well as the strong relationship between δ¹³C-DOC and chlorophylla, suggest that in situ production was an important component of the DOC pool. We hypothesize that uncharacteristically calm wind conditions during sampling may have promoted phytoplankton settling, removing autotrophs, from the water column, but leaving behind a dissolved biogeochemical signature. Interpretation of carbon dynamics may be confounded by spatial and temporal decoupling of producers and consumers from biogeochemical indicators.     

Natural Environmental Changes versus Human Impact in a Florida Estuary (Rookery Bay, USA)

Assessing the impact of climate change and anthropogenic activity on Florida coastal areas requires a thorough understanding of natural climate variability. The available instrumental record, however, is too short and too limited to capture the full range of natural variability. In order to provide additional data on the natural state of the climate system and to evaluate the influence of human impact, we reconstructed climatic and environmental changes of the past 300 years. Pre- (before 1900 ad) and post-human impact conditions were compared in Rookery Bay, a subtropical, southern Florida estuary and its bordering wetland system. Biomarkers from terrestrial and aquatic environments were used to reconstruct temperature, runoff, and aquatic productivity. Pre-anthropogenic conditions before 1750 ad indicate a relatively large contribution of mangrove-derived organic matter, locally decreasing at the end of this period. After 1750 ad follows a relatively stable period in which biomarker concentrations indicate relatively low levels of runoff and aquatic production. Enhanced anthropogenic activities, such as land clearance and hydrological alterations, end this period of stability by altering the hydrological conditions. This leads to a more dynamic system which is more sensitive to disturbances of vegetation and drainage, as evidenced by peak terrestrial biomarker fluxes during the twentieth century. These episodes of enhanced runoff resulted in eutrophication and algal blooms in Rookery Bay. Natural climate phenomena, such as a positive AMO phase and hurricane activity, might have added to ongoing processes during the twentieth century.     

Hydrogeochemistry and dissolved inorganic carbon isotopic composition on karst groundwater in Maolan, southwest China

The forest ecosystem in the Maolan karst forest, southwest China is the only concentrated, intact, and relatively stable karst forest ecosystem which has survived in the area at the same latitude in the world, and is a valuable karst forest plant resource as well. Groundwater samples from Maolan karst forest were collected from wells and springs during summer; and concentrations of major ions and dissolved inorganic carbon (DIC) isotopic compositions were measured. The pH values range from 7.2 to 8.3 results from the dissolution of carbonate, HCO₃ ⁻ is the dominant species of DIC in groundwater. Calcium and HCO₃ ⁻, followed by Mg²⁺ and SO₄ ²⁻ dominate the chemical composition of major ions in the groundwaters. Groundwater samples have δ¹³C values in the range from −8.1‰ to −16.6‰, which are lower than that of the other karst city groundwaters in the southwest China. Combining δ¹³C_DIC ratios with measurements of HCO₃ ⁻ and pH clearly distinguishes the principal processes underlying the geochemical evolution of groundwater in Carboniferous carbonate aquifers, where processes can be both degradation of organic matters in the soil and the carbonate dissolution.     

Abundance,distribution, and fluxes of dissolved organic carbon (DOC) in four small sub-tropical rivers of the Tampa Bay Estuary (Florida,USA)

The delivery of organic carbon (C) from rivers to the coastal ocean via estuaries is recognized as an important component of the global C budget however, smaller river systems are often overlooked and modern flux estimates are not very different from historical estimates. Here, the seasonal (wet vs. dry) concentration and fluxes of dissolved organic C (DOC) were measured in five small sub-tropical rivers that drain into the Tampa Bay (FL, USA) estuary. DOC distributions were highly variable among riverine, mesohaline, and marine end-member samples in all river catchments and no significant differences were observed among or between DOC concentrations with respect to river catchment, season, or year of sampling. In general, DOC mixed non-conservatively during the wet seasons, and conservatively during the dry seasons, with the estuarine reaches of each river serving as a sink of DOC. Fluxes were strongly tied to discharge irrespective of season, and the estuaries removed 15–65% of DOC prior to export to coastal Bay and Gulf of Mexico waters. DOC concentrations were similar to others reported for low-elevation sub-tropical rivers, and a combination of elevation, residence time, and climate appear to control the abundance and variability of DOC in sub-tropical vs. tropical river systems. The characterization of DOC in small, sub-tropical rivers, which share characteristics with both their temperate and tropical counterparts, is critical for quantitatively constraining the importance of these systems in local-to-regional scale ocean C budgets. In addition to geomorphic properties, the role of past, present, and future land cover and other environmental change in small coastal rivers also exerts control on the quantity and flux of DOC in these systems.     

Influence of a reservoir chain on the transport of riverine inorganic carbon in the karst area

The Wujiang River is an important tributary to the Changjiang River that has been intensively impounded for hydropower exploitation. To understand the potential impact of reservoir construction on the riverine inorganic carbon transport, seasonal longitudinal sampling was conducted in four reservoirs Hongjiadu (HJD), Dongfeng (DF), Suofengying (SFY) and Wujiangdu (WJD) along the Wujiang River from April 2006 to January 2007. Results indicated that damming the river induced an obvious discontinuity of water chemistry in the warmer seasons. δ ¹³C of dissolved inorganic carbon (DIC) ranged from ?3 to ?11.4 ‰, likely as the results of photosynthesis, respiration and carbonate weathering. During periods of thermal stratification, the addition of CO₂ from respiration to hypolimnion and the deep water release for hydropower generation led to higher pCO₂ downstream, as well as ¹³C depletion in DIC and undersaturated to calcite. An estimate of DIC budget indicated that only DF reservoir was the sink for DIC while reservoirs HJD, SFY and WJD were the sources for DIC. However, when the retained water was taken into account, for the reason of water storage occurring mainly in HJD and DF, all reservoirs became the sources for DIC with exporting rates of 26.68, 7.97, 6.22 and 11.80 % for HJD, DF, SFY and WJD, respectively.     

Distribution and habitat partitioning of immature bull sharks (Carcharhinus leucas) in a Southwest Florida estuary

The distribution and salinity preference of immature bull sharks (Carcharhinus leucas) were examined based on the results of longline surveys in three adjacent estuarine habitats in southwest Florida: the Caloosahatchee River, San Carlos Bay, and Pine Island Sound. Mean sizes were significantly different between each of these areas indicating the occurrence of size-based habitat partitioning. Neonate and young-of-the-year animals occurred in the Caloosahatchee River and juveniles older than 1 year occurred in the adjacent embayments. Habitat partitioning may reduce intraspecific predation risk and increase survival of young animals. Classification tree analysis showed that both temperature and salinity were important factors in determining the occurrence and catch per unit effort (CPUE) of immatureC. leucas. The CPUE of <1 year oldC. leucas was highest at temperatures over 29°C and in areas with salinities between 7‰ and 17.5‰ Although they are able to osmoregulate in salinities from fresh to fully marine, youngC. leucas may have a salinity preference. Reasons for this preference are unknown, but need to be further investigated.     

峰丛洼地自然封育过程岩溶水溶解无机碳的变化——以桂林丫吉试验场为例

以桂林丫吉试验场为例,检验植被恢复对岩溶碳汇的影响作用。上世纪80年代,丫吉试验场峰丛洼地的植被受砍伐干扰,地表以草地居多,此后施行自然封山育林,植被经二十多年的封育后,现在变成为灌木林,土壤中植物根系呼吸和微生物异养呼吸增强,土壤空气中CO2含量上升,岩溶作用增强,泉水输出的无机碳通量增加。通过建立系统的水化学混合模型,将泉水的无机碳通量分解为原水输出和降雨补给引起的新水输出。在一次典型的强降雨过程,S31岩溶泉原水输出量占总量的65%~83%,而降雨补给引起的新水无机碳输出通量较少,且不能反映生态环境的变化,因此应以原水中溶解无机碳的浓度衡量整个生态环境对岩溶作用的影响。长期的观测表明由于植被的改变导致原水输出的无机碳含量提高了27%,而原水在岩溶泉的年流量中所占的比例高达72%~84%,其中由植被演化造成岩溶碳汇增加的幅度为19%~23%。      

Distribution of carbon in a tropical hypersaline estuary,the Casamance (Senegal,West Africa)

The Casamance estuary, on the coast of Senegal, is an inverse hypersaline estuary: salinity increases landward, and dry season salinity values are up to 172 psu due to the evaporation of seawater. Dissolved inorganic carbon (DIC) concentrations decreased landward as a negative linear function of salinity. Thermodynamic modelling and the absence of CaCO₃ in the sediments indicate that this loss of DIC was not due to calcite precipitation in the main water body. The innermost, almost landlocked, waters contained high phytoplankton biomass (50–300 μg chl I^?1) and high concentrations of allochthonous dissolved organic carbon. Photosynthetic uptake of DIC and subsequent particulate organic carbon sedimentation is proposed as hypothetical explanation of the relationship between DIC and salinity; localized overheating in shallow waters might also be involved.     

Evaporation, precipitation, and associated salinity changes at a humid, subtropical estuary

The distilling effect of evaporation and the diluting effect of precipitation on salinity at two estuarine sites in the humid subtropical setting of the Indian River Lagoon, Florida, were evaluated based on daily evaporation computed with an energy-budget method and measured precipitation. Despite the larger magnitude of evaporation (about 1,58 mm yr⁻¹) compared to precipitation (about 1,180 mm yr⁻¹) between February 2002 and January 2004, the variability of monthly precipitation induced salinity changes was more than twice the variability of evaporation induced changes. Use of a constant, mean value of evaporation, along with measured values of daily precipitation, were sufficient to produce simulated salinity changes that contained little monthly (root-mean-square error = 0.33‰ mo⁻¹ and 0.52‰ mo⁻¹ at the two sites) or cumulative error (<1‰ yr⁻¹) compared to simulations that used computed daily values of evaporation. This result indicates that measuring the temporal variability in evaporation may not be critical to simulation of salinity within the lagoon. Comparison of evaporation and precipitation induced salinity changes with measured salinity changes indicates that evaporation and precipitation explained only 4% of the changes in salinity within a flow-through area of the lagoon; surface water and ocean inflows probably accounted for most of the variability in salinity at this site. Evaporation and precipitation induced salinity changes explained 61% of the variability in salinity at a flow-restricted part of the lagoon.     

Groundwater flood of a river terrace in southwest Wisconsin,USA

Intense rainstorms in 2008 resulted in wide-spread flooding across the Midwestern United States. In Wisconsin, floodwater inundated a 17.7-km² area on an outwash terrace, 7.5 m above the mapped floodplain of the Wisconsin River. Surface-water runoff initiated the flooding, but results of field investigation and modeling indicate that rapid water-table rise and groundwater inundation caused the long-lasting flood far from the riparian floodplain. Local geologic and geomorphic features of the landscape lead to spatial variability in runoff and recharge to the unconfined sand and gravel aquifer, and regional hydrogeologic conditions increased groundwater discharge from the deep bedrock aquifer to the river valley. Although reports of extreme cases of groundwater flooding are uncommon, this occurrence had significant economic and social costs. Local, state and federal officials required hydrologic analysis to support emergency management and long-term flood mitigation strategies. Rapid, sustained water-table rise and the resultant flooding of this high-permeability aquifer illustrate a significant aspect of groundwater system response to an extreme precipitation event. Comprehensive land-use planning should encompass the potential for water-table rise and groundwater flooding in a variety of hydrogeologic settings, as future changes in climate may impact recharge and the water-table elevation.     

Distribution and migrations of the prawnPalaemon longirostris in the Mira River estuary (southwest Portugal)

Palaemon longirostris was sampled monthly at 12 sites in the Mira River estuary (southwest Portugal) from October 1990 to September 1991. Animals were counted, measured, and sexed. The estuarine distribution of prawns appeared to follow the salinity displacement, the animals being found at river stations during summer and autumn when saline encroachment up the estuary was greater. During winter and spring when freshwater input from the river was greatest, and thus moving the salinity gradient toward the mouth, the prawns migrated downstream to brackish areas. Ovigerous females were collected only from estuarine areas (January to August), suggesting that reproduction does not take place in freshwater habitats. Higher percentages of females than males were generally observed. Females, particularly ovigerous ones, were larger than males.