A Comparison of Three Methods to Collect Submerged Aquatic Vegetation in a Shallow Lake

Two boat-based and one in-water sampling method have been used to collect submerged aquatic vegetation (SAV) as part of a long-term monitoring program in Lake Okeechobee, Florida, USA. The boat-based methods consisted of collecting SAV with a ponar dredge, used only to collect Chara, and an oyster tongs-like rake apparatus, used to collect all SAV. The in-water method involved use of a 0.5 m² PVC quadrat frame deployed by a diver. During summer 2002, SAV biomass samples were collected using all three methods at various sites in the lake to compare between-methods sampling precision. Sites used for these comparisons were selected based on plant type, plant density and sediment type. Statistical comparisons indicated that there were significant (p ≤ 0.05) biomass differences in 8 of 15 possible pairwise comparisons between sampling method biomass means. In four of the eight comparisons, significantly higher biomass mean values were obtained using the quadrat frame. In three of the remaining four comparisons, significantly higher biomass mean values were obtained with the rake apparatus. For the fourth comparison, a significantly higher biomass mean value was obtained with the ponar dredge. Three of the four relationships between SAV biomass collected by the rake and the quadrat and the rake and the quadrat/ponar dredge were statistically significant, linear and explained between 67 and 78% of the biomass variability. There were no significant differences between regression coefficients or elevations for these relationships, therefore these regressions estimated the same population regression. The population regression coefficient was 0.95, suggesting that the quadrat and ponar over-sampled relative to the rake, but the amount of this over-sampling was very small. Since there was no consistent pattern in the sampling method which yielded the significantly different biomass values and there were no significant differences in sampling precision across a range of plant species, plant densities and two sediment types, the boat-based rake method appears to be a suitable replacement for the previously used ponar dredge and quadrat methods, when in-lake measurements are not practical.  

洪泽湖湖滨带表层沉积物氮、磷、有机质分布及污染评价

洪泽湖作为中国第四大淡水湖泊，是江苏北部地区重要的水源地，同时也是南水北调东线工程的重要调蓄湖泊之一，研究其湖滨带表层沉积物氮、磷、有机质的污染情况对维持洪泽湖水安全和生物多样性具有重要现实意义。基于2020年8月于洪泽湖湖滨带采集的43个表层（0~10 cm）沉积物样品，分析了总氮（TN）、总磷（TP）和有机质（OM）含量的空间分布特征及相关性，并运用综合污染指数法和有机污染指数法评价其污染程度。结果表明，洪泽湖湖滨带表层沉积物TN、TP、OM含量范围分别为232~2 152 ，123~439，0.91~18.65 mg/kg，均值分别为985，276，10.93 mg/kg；空间分布上均表现为东部大堤、成子湖和西部区域的TN、TP、OM含量高于过水通道；Pearson相关性分析显示，表层沉积物中ω(OM)与ω(TN)（r=0.705，P<0.01）、ω(TN)与ω(TP)（r=0.504，P<0.01）呈显著正相关；洪泽湖湖滨带表层沉积物综合污染指数范围为0.45~1.88，平均值为0.93，有机污染指数范围为0.001~0.221，平均值为0.067，2种评价方法均显示洪泽湖湖滨带表层沉积物中TN、TP、OM整体处于清洁—轻度污染状态。  

基于O/E模型的浅水湖泊生态系统健康评价

以长江中下游阻隔型浅水湖泊为研究对象,分析了1998—2018年116湖次底栖动物野外调查数据,构建了基于预测模型的观测物种组成/期望物种组成(O/E)指数健康评价指标体系,评价了长江中下游浅水湖泊的底栖动物物种组成完整性。O/E指数模型评价结果显示,在物种采集概率(Pc)>0阈值条件下的O/E₀模型预测得到的监测湖泊期望丰富度,大于Pc≥0.5条件下的O/E₅₀模型预测得到的期望丰富度。模型控制自然梯度后的O/E₀值、O/E₅₀值与原始模型O/E值差异不大,但原始模型误差均大于控制自然梯度的O/E模型误差,且控制自然梯度的O/E₅₀模型误差为0,因此,O/E₅₀模型是开展湖泊健康评价的最有效指数模型。健康评价结果表明,长江中下游湖泊健康状况一般,仅有约20%处于健康水平,约25%的湖泊健康状况较差。O/E指数和富营养化因子相关关系显著,表明O/E指数能够反映湖泊营养状态变化。该O/E指数模型可应用于浅水湖泊生态系统健康评价,为浅水湖泊修复和可持续发展提供科学基础。  

基于底栖动物的水质生物学评价——以江苏骆马湖为例

基于2018年1—11月骆马湖水质和底栖动物逐月监测数据，利用Goodnight指数（GBI）、生物学污染指数（BPI）、Shannon Wiener指数（H′）等生物学指数对水质现状进行了评价。结果表明，骆马湖ρ（总氮）年均值为2.31 mg/L，ρ（总氮）和ρ（溶解氧）呈先下降后上升趋势；ρ（总磷）年均值为0.05 mg/L，先上升于8月达到峰值（0.15 mg/L）后下降；高锰酸盐指数呈先上升后下降趋势；ρ（氟离子）呈逐渐下降趋势，水温和电导率存在明显季节变化，pH值呈逐渐升高趋势。共鉴定出底栖动物27种，其中软体动物5种，环节动物7种，节肢动物15种。铜锈环棱螺（Bellamya aeruginosa）、红裸须摇蚊（Propsilocerus akamusi）、纹沼螺（Parafossarulus striatulus）、苏氏尾鳃蚓（Branchiura sowerbyi）、霍甫水丝蚓（Limnodrilus hoffmeisteri）、多巴小摇蚊（Microchironomus tabarui）和中国长足摇蚊（Tanypus chinensis）是现阶段优势种。全湖底栖动物年均密度为174.5个/m²，年均生物量为24.93 g/m²，表现出明显的时空差异。水质评价结果表明，骆马湖水环境处于中污染状态。结合近年来研究结果，骆马湖底质荒漠化现象趋于好转，但富营养化趋势正在加深。