A COMPARISON OF THREE METHODS FOR MEASURING RECENT RATES OF SEDIMENT ACCUMULATION1

ABSTRACT: The determination of sediment accumulation rates is important in understanding how these materials are affecting lakes and reservoirs ecosystems. In this study three methods were used to estimate sediment accumulation rates in the impounded backwater lakes behind Lock and Dam Nos. 8 and 9 on the upper Mississippi River. The three methods were: 1) a “spud” survey, 2) a survey of bottom contours, and 3) the use of fallout cesium-137. The field use of these three methods of determining sediment accumulation and the potential errors and merits involved in each method are discussed. The results from the field study in backwater areas along the upper Mississippi River showed the survey of bottom contour method gave the lowest rate of sediment deposition and the ¹³⁷Cs method gave the highest rates. Sediment accumulation rates from 0 to 7.8 cm per year were measured in the study area. All three methods are useful and have unique characteristics for determining rates and patterns of sediment accumulation. Thus the choice of a method to be used in a sediment survey is dependent on the type of information needed and the time available.     

ARE SHORT-TERM ENVIRONMENTAL ACTION PROGRAMS POSSIBLE? -THE INLAND LAKE PROJECT EXPERIENCE1

The public clamor for repair and protection of the environment from damages, real or perceived, is growing daily. People are demanding remedial programs now; they appear willing to support long-range fundamental research in environmental areas (such as eutrophication research) as long as action programs (such as lake renewal) are undertaken too. Are short-term, remedial, environmental action programs possible? The experiences of the Inland Lake Demonstration Project afford an opportunity to evaluate one kind of action-oriented response. Some special types of problems are likely to be common to any environmental-resource action program. Recognition and anticipation of these difficulties when organizing action programs should facilitate successful implementation.     

RELATIONSHIPS BETWEEN WATER QUALITY AND PHOSPHORUS CONCENTRATIONS FOR PUGET SOUND REGION LAKES1

Regression relationships were developed between summer mean total phosphorus (P) concentrations in near-surface water and both chlorophyll a concentrations and Secchi disc transparency for Puget Sound region lakes. Total P concentrations in the lakes studied ranged from 7 to 66 μ/L. The relationship between total P and chlorophyll a, based on data from 69 lakes, explained 57 percent of the variance in chlorophyll a. Predicted chlorophyll a concentrations and 95 percent confidence intervals ranged from 1 ⁺³_-0.5μg/L for 7 μg/L P to about ⁺³⁵_-10μ/L for 66 μ/L P. The relationship between total P and Secchi disc, based on data from 71 lakes, explained 53 percent of the variance in Secchi disc. Predicted Secchi disc transparencies and 95 percent confidence intervals ranged from 5.5 ^+5.5_-3.0 m for 7 μ/L P to 1.4 ^+1.5_-0.7 m for 66 μ/L P.     

A Sensitivity and Error Analysis Framework for Lake Eutrophication Modeling1

ABSTRACT: A framework for sensitivity and error analysis in mathematical modeling is described and demonstrated. The Lake Eutrophication Analysis Procedure (LEAP) consists of a series of linked models which predict lake water quality conditions as a function of watershed land use, hydrolgic variables, and morphometric variables. Specification of input variables as distributions (means and standard errors) and use of first-order error analysis techniques permits estimation of output variable means, standard errors, and confidence ranges. Predicted distributions compare favorably with those estimated using Monte-Carlo simulation. The framework is demonstrated by applying it to data from Lake Morey, Vermont. While possible biases exist in the models calibrated for this application, prediction variances, attributed chiefly to model error, are comparable to the observed year-to-year variance in water quality, as measured by spring phosphorus concentration, hypolimnetic oxygen depletion rate, summer chlorophyll-a, and summer transparency in this lake. Use of the framework provides insight into important controlling factors and relationships and identifies the major sources of uncertainty in a given model application.     

Estimation of Critical Loads of Acidity for Lakes in Northeastern United States and Eastern Canada

The New England Governors and Eastern Canadian Premiers (NEG/ECP) adopted the Acid Rain Action Plan in June 1998, and issued a series of action items to support its work toward a reduction of sulfur dioxide (SO₂) and nitrogen oxide (NO_x) emissions in northeastern North America. One of these action items was the preparation of an updated critical load map using data from lakes in the NEG/ECP area. Critical load maps provide a more complete index of the surface water sensitivity to acidification. Combined sulfur and nitrogen critical loads and deposition exceedances were computed using Henriksen's Steady-State Water Chemistry (SSWC) model. Results show that 28% of all 2053 lakes studied have a critical load of 20 kg/ha/year or less, making them vulnerable to acid deposition. Emission reductions, and more specifically SO₂ emission reductions have proven beneficial because critical loads were exceeded in 2002 for 12.3% of all studied lakes. Those lakes are located in the more sensitive areas where geology is carbonate-poor. Of these lakes, 2.9% will never recover even with a complete removal of SO₄ deposition. Recovery from acidification for the remaining 9.4% of the lakes will require additional emission SO₂ reductions.     

Potential Effects of Metals in Reacidified Limed Water Bodies in Norway and Sweden

The goal of this work was to assess risk of chemical andbiological effects of metals in reacidified, limed water bodiesin Norway and Sweden. The risk assessment is based on aliterature review and evaluations of water chemical data fromthe 1995 Nordic Lake Survey. Compared to the pre-liming period,it us unlikely that enhanced remobilization of inorganicaluminium (Al) or other toxic metals (metal bomb hypothesis)from the catchment, the lake sediment and/or the streambed willoccur when limed waters reacidify. Rather, the concentrationsin surface waters are expected to be lower than before limingstarted, because of reduced atmospheric inputs of both strongacids and metals as Cd, Hg, Pb, and Zn during the last 10–20 yr. The concentrations in lakes relative to the biologicaleffect levels, as well as the chemical properties of thedifferent metals suggest that the potential biological risksassociated to reacidification of limed lakes decrease in theorder Al > Cd > Pb. The risks associated with Cr, Cu, Fe, Mn, Ni and Zn are very low and do not have to be consideredexcept in waters with known concentrations larger than the lowest biological risk level. Such waters are very rare (<2%). Aluminium is the metal that should be used to set the limit for judging the risk of biological damage due to reacidification of limed surface waters.     

云南九大高原湖泊水体总α、总β调查与评价

报道了对云南九大高原湖泊水体中总α、总β放射性水平的调查结果,并对调查结果进行了分析比较,为开展水体的环境辐射评价提供一定的依据。调查结果表明,这九大高原湖泊水体的总α、总β放射性水平属正常本底水平。     

我国东部浅水湖泊水生态效应特征

为探究我国东部浅水湖泊生态系统的时空异质性及其演替的响应指标,基于东部浅水湖泊长时间序列（1986-2014年）的监测数据,分析了不同湖泊类型的水质和浮游植物群落分布特征,并综合运用稳态转换理论和典范对应分析方法（CCA）,研究了富营养化湖泊浮游植物群落的演替特征以及响应因子.结果表明:①从水系上看,太湖水系湖泊的水质最差,ρ（TP）、ρ（TN）和ρ（Chla）最高,分别为（0.276±0.606）（3.563±1.430）mg/L和（14.801±10.117）μg/L,SD（透明度）为（0.486±0.272）m;从水文连通性上看,湖泊的水质为通江湖泊>非通江湖泊>阻隔湖泊.②空间分布上,湖口以下干流浮游植物密度最高,为2.674×107 L-1.蓝藻门为东部浅水湖泊的优势种群,密度最高达1.897×107 L-1,绿藻门和硅藻门次之,黄藻门最少,仅为3.951×103 L-1.③东部浅水湖泊生态系统演替发生在ρ（Chla）为5.21~10.57 μg/L阈值范围内.④以东部典型湖泊-太湖为例,浮游植物群落分别在1997-1998年和2000-2001年两个时间梯度达到最大值.EC（电导率）和ρ（TN）是影响太湖浮游植物群落分布的显著因子.研究显示,随着东部浅水湖泊水质恶化,浮游植物群落结构特征发生突变,导致其生态系统发生演替,预防东部浅水湖泊生态系统演变应严控EC和ρ（TN）.      

温度对湖泊沉积物中沉水植物残体厌氧分解的影响

淡水湖泊水生植物残体的腐烂分解过程为沉积物中的异养微生物提供了重要的碳源,但是目前关于温度对沉水植物残体有机质分解的影响研究还不够深入.本研究通过室内微宇宙模拟实验,研究了4℃和25℃时马来眼子菜残体在沉积物中厌氧分解特征及其主要的微生物代谢途径.结果表明,温度对马来眼子菜残体的分解影响显著,25℃实验组沉积物中总有机碳（TOC）和纤维素去除率显著高于4℃实验组.25℃实验组沉积物初始腐殖质占TOC比例为18.23%±1.47%,90 d后达到约46%,这说明微生物对马来眼子菜残体的分解促进了沉积物腐质化.此外,温度升高促进了纤维素降解细菌（如拟杆菌门,Bacteroidetes）的生长繁殖,且硫酸盐还原细菌（如GOUTA19、脱硫球菌属（Desulfocuccus）、LCP-6、HB118）和铁还原细菌（如地杆菌属,Geobacter）是沉积物中主要的优势菌种.在25℃条件下,微生物硫酸盐还原、铁还原和产甲烷作用占马来眼子菜残体厌氧代谢的比例分别达到37.3%、27.8%和10.3%.综上所述,本研究表明温度升高促进了沉积物中马来眼子菜残体的厌氧分解,且微生物硫酸盐还原、铁还原和产甲烷过程在其厌氧分解过程中发挥了重要作用.     

硅藻群落指示的近50年来大理西湖湖泊生态系统演变规律

近年来,增强的人类活动使得云南部分湖泊生态系统发生退化,由草型清水态向藻型浊水态转变.全球变化背景下,了解湖泊生态系统演变规律是进行有效管理的前提,具有重要的科学意义.本研究以云南大理州小型浅水湖泊西湖为例,通过对沉积物硅藻群落和理化指标的分析,探讨了20世纪60年代中期以来大理西湖环境演变历程.结果表明,大理西湖生态系统在近50年发生了明显的稳态转换,以2000年为节点,硅藻群落从2000年前偏好贫营养环境的底栖附生种Cocconeis placentula、Staurosira construens、Gomphonema angustum和Achnanthidium minutissimum为优势种的状态,逐渐演替为偏好中营养环境的底栖附生硅藻Encyonopsis microcephala和Navicula cryptocephala及偏好富营养环境的浮游硅藻Cyclotella atomus、Cyclotella meneghiniana、Stephanodiscus hantzschii和Aulacoseira granulata为主导的状态.时间序列的主成分分析表明,硅藻群落主要响应了营养的变化.冗余分析结果也证实营养盐富集是大理西湖硅藻群落长期演化的主要驱动因素.本文论述了近50年来大理西湖流域气候变化和开发活动（农业围垦、化肥施用、畜牧养殖和渔业养殖等）促使湖泊营养盐持续积累,浮游藻类大量繁殖,湖泊内部生产力显著提高,湖泊生态系统逐渐向藻型浊水态转变的演化特征.