Stable isotope enrichment in muscle,liver,and whole fish tissues of brown-marbled groupers(Epinephelus fuscoguttatus)

Introduction:The purpose of this study was to assess enrichments in stable carbon and nitrogen isotopes(δ^(13)C andδ^(15)N)in brown-marbled groupers(Epinephelus fuscoguttatus),a marine fish that has been widely used in aquaculture.Stable isotope analysis has been used to evaluate dietary sources and the trophic position of fish.There is the need to better understand the pattern of isotope enrichment between consumers and diets under laboratory conditions.Methods:We studied the changes in stable carbon and nitrogen isotopes of juvenile brown-marbled groupers during a feeding experiment in 2009.Fish were grown in aquaria and fed a sole source of protein for 56 days and analyzed forδ^(13)C andδ^(15)N ratios in whole fish,muscle,and liver tissues.Results:At the end of the 56-day feeding experiment,fish grew to an average of 55.6 g from an average of 22.5 g.Compared to the dietary isotope compositions,whole fish and muscle tissues of the juvenile groupers were enriched inδ^(13)C by 1.6 and 0.5%,while the liver was depleted by 1.3%.Theδ^(15)N enrichments were 1.6%for whole fish,1.3%for muscle,and 1.0%for liver.Except for liver,δ^(15)N isotope values increased significantly with time.Conclusions:The small change inδ^(13)C between the diet and fish suggests that little isotope alteration is occurring during the assimilation of dietary carbon.This provides a basis for estimates of the importance of different sources of dietary components when contrasted with the isotope values from a formulated diet with known isotope values of the different components.The smaller than expectedδ^(15)N enrichment in all tissue suggests that isotope values from a wild fish sample may not always reach isotope equilibrium with the current diet,and an inference about recent dietary sources and an estimate of the consumer’s trophic position should be evaluated with caution.

辐射变暗和透明度降低共同加剧湖泊水下变黑

人类活动和气候变化造成到达地表太阳辐射降低(即辐射变暗)和水体透明度下降,两者共同作用深刻影响到水生生态系统水下光环境.全国116个太阳辐射观测站和839个日照时数观测站长期观测数据显示,2000年之后年均地表太阳辐射和日照时数比20世纪60年代分别下降了5.8%和7.9%,呈现显著下降趋势.与此同时,20世纪80年代和2006~2010年两次全国湖泊调查和历史文献数据分析发现,170个湖泊透明度平均值由1995年之前的1.80±2.19 m下降到2005年之后的1.28±1.82 m,遥感反演发现641个面积大于10 km2的湖泊透明度平均值由1985~1990年的1.26±0.62 m降低到2005~2010年的1.14±0.66 m.辐射变暗和透明度降低共同造成全国湖泊平均真光层深度范围内可利用的光合有效辐射量降低10%左右,并且透明度降低对湖泊水下光合有效辐射降低的贡献超过80%.文献综合分析进一步显示,全球湖库、海湾和近海水体均普遍存在透明度下降,水下变暗甚至变黑的事实,其势必深刻影响到水生生态系统各种物理、化学和生物过程以及生物多样性、生态系统服务功能和服务价值.

Phosphorus removal in small constructed wetlands dominated by submersed aquatic vegetation in South Florida, USA

Aims Free-surface flow-constructed wetland is a powerful means for the reduction of contaminants from agricultural runoff.Wetlands dominated by submerged aquatic vegetations(SAVs)may take up nutrients,particularly phosphorus(P),from surface flow with high efficiency.The objective of this study was to assess P removal performance by the SAV community under high and low P concentrations.Methods Weekly or biweekly inflow and outflow water samples were collected from four small constructed wetlands(test cells)planted with SAV in South Florida,USA,between September 1999 and September 2001.These test cells were divided into two groups,with the north test cells receiving a higher inflow total phosphorus(TP)concentration(average=75 lg l^(-1))than the south test cells receiving a lower TP concentration(average=23 lg l^(-1)).Limerock(LR)berms were installed in two of these test cells to allow an evaluation of the efficiency of this physical barrier to enhance wetland performance.Important findings North test cells displayed high TP removal of;60%while the removal efficiency of the south test cells was only;20%.Soluble reactive phosphorus concentrations in both north and south test cells were sequestered down to near-detection limit.High removal efficiencies for particulate phosphorus were also observed in the north test cells.The LR berms at the two test cells were found to be associated with decreases of an average TP removal of 2 lg l^(-1).Outflow TP concentration did not increase with inflow TP concentration,but increased with nominal hydraulic loading rates.Findings from this study demonstrated high P removal from inflow water containing high TP concentration by the SAV wetland and the importance of hydraulic regime to wetland performance.

Environmental stress and eutrophication in freshwater wetlands: evidence from carbon and nitrogen stable isotopes in cattail (Typha domingensis Pers.)

Background:Florida’s Everglades is a vast freshwater peatland that has been impacted by the alterations of hydrological pattern and water quality which led to changes in plant species composition and biodiversity.In this study,carbon and nitrogen stable isotopes(δ13C andδ15N)in cattail(Typha domingensis)are evaluated as indicators of environmental changes in the Everglades wetlands along nutrient and hydrological gradients represented by reference sites with total phosphorus(TP)<10μg L−1,transition sites with TP≥10μg L−1<20μg L−1 and impacted sites with TP≥20μg L−1 which differed in hydrology or habitats(marsh and canal).Results:Cattailδ13C values decreased significantly from reference(–24.1‰),transition(–26.8‰)to the impacted sites(–28.2‰).In contrast,δ15N values increased significantly from reference(–5.2‰),transition(2.4‰)to the impacted site(5.9‰).In response to a poor hydrological condition,cattail in marsh area displayed 13C enrichment(–26.0‰)and 15N depletion(0.2‰).By contrast,cattail grown in the canal sites with favorable hydropattern displayed 13C depletion(–27.6‰)and 15N enrichment(5.9‰)from the canal sites with more favorable hydrological condition.Conclusions:The different patterns for the changes inδ13C andδ15N in cattail suggested that increased nutrients led to increased stomatal conductance and 13C fractionation during carbon uptake and decreased 15N fractionation with increasing nitrogen demand while poor hydrological condition coupled with low nutrients led to reduced plant growth indicated by higherδ13C and lowerδ15N values.Findings from this study suggested thatδ13C in emerged macrophytes such as cattail can be used as an indicator for environmental stress whileδ15N is a robust indicator for wetland eutrophication.

Carbon pool trends and dynamics within a subtropical peatland during long-term restoration

Introduction:The Florida Everglades has undergone significant ecological change spanning the continuum of disturbance to restoration.While the restoration effort is not complete and the ecosystem continues to experience short duration perturbations,a better understanding of long-term C dynamics of the Everglades is needed to facilitate new restoration efforts.This study evaluated temporal trends of different aquatic carbon(C)pools of the northern Everglades Protection Area over a 20-year period to gauge historic C cycling patterns.Dissolved inorganic C(DIC),dissolved organic C(DOC),particulate organic C(POC),and surface water carbon dioxide(pCO2(aq))were investigated between May 1,1994 and April 30,2015.Results:Annual mean concentrations of DIC,DOC,POC,and pCO2(aq)significantly decreased through time or remained constant across the Water Conservation Areas(WCAs).Overall,the magnitude of the different C pools in the water column significantly differed between regions.Outgassing of CO2 was dynamic across the Everglades ranging from 420 to 2001 kg CO2 year−1.Overall,the historic trend in CO2 flux from the marsh declined across our study area while pCO2(aq)largely remained somewhat constant with the exception of Water Conservation Area 2 which experienced significant declines in pCO2(aq).Particulate OC concentrations were consistent between WCAs,but a significantly decreasing trend in annual POC concentrations was observed.Conclusions:Hydrologic condition and nutrient inputs significantly influenced the balance,speciation,and flux of C pools across WCAs suggesting a subsidy-stress response in C dynamics relative to landscape scale responses in nutrient availability.The interplay between nutrient inputs and hydrologic condition exert a driving force on the balance between DIC and DOC production via the metabolism of organic matter which forms the base of the aquatic food web.Along the restoration trajectory as water quality and hydrology continues to improve,it is expected that C pools will respond accordingly.

Initial response of fish trophic niche to hydrological alteration in the upstream of Three Gorges Dam

Introduction:Damming is one of the dramatic impacts to river food webs due to habitat fragmentation and changes in the hydrological regimes.The world’s largest dam,the Three Gorges Dam(TGD),has been constructed in the middle of Yangtze River since 2003.The objective of this study was to understand the effects of altered hydrological regime on the trophic structure of fish food web along the hydrological gradient in the TGD.Methods:Fish samples were collected from an upstream,a midstream and a downstream site of the Yangtze River upstream of the TGD in May and September of 2004.Muscle tissue of each fish species was determined for stable isotopic compositions(δ^(13)C and δ^(15)N)which were used to calculate isotope-based Bayesian community-wide trophic metrics.Results:Stable isotope trophic niche analysis reveals reduced utilization of basal resource and trophic niche space at the midstream and downstream sites.By contrast,community trophic diversity and species redundancy were higher at the downstream than the upstream and midstream,likely as the result of reduced the spectrum of basal resources.These findings suggested that the negative impacts on the overall trophic niche space from reduced flow,increased water depth and stagnancy occurred only one year after the completion of the TGD.Conclusions:Altered hydrological regimes posed multiple impacts to the aquatic food web.Reduced flow and increased water depth within TGD has posed initial effects to the fish community trophic structure.Further collections ana analysis of ecological data to compare the fish trophic structure revealed in this study are needed to assess the long-term impacts of TGD on fish community structure and resources utilization.