城市化背景下白洋淀入湖营养盐负荷模拟研究

过量的营养盐输入导致白洋淀富营养化程度较高。雄安新区建设伴随着快速城镇化进程,将可能进一步增加入湖营养盐负荷。为摸清新区建设背景下白洋淀入湖营养盐负荷的变化趋势及削减量,基于入湖营养盐负荷模型计算了历史不同时期（1995-2015年）白洋淀入湖营养盐盐负荷,预测了土地利用、农业管理和污水处理系统变化下入湖营养盐负荷的变化趋势。结果表明,白洋淀历史时期入湖总氮和总磷年平均负荷分别为2018 t和313 t,主要来源分别是耕地和畜禽粪便排放。就土地利用变化而言,以2010年为基准,2050年白洋淀入湖总氮和总磷负荷在建设用地快速增长（RAP）情景下增长率最高,分别增长了56%和60%,主要原因在于城镇人口增加,从而增加了畜禽需求量和生活污水排放。就农业管理而言,削减化肥使用有利于降低入湖总氮负荷,控制畜禽粪便排放更有利于入湖总磷负荷的降低。2050年,生活污水将成为白洋淀入湖营养盐的重要来源,因此,在制定未来社会经济发展路径时,应重点提高农村地区生活污水收集率和处理效率。PCLake模型对不同入湖负荷下湖泊营养状态演变的模拟发现,削减入湖总磷负荷是白洋淀水质恢复的关键。白洋淀水质达到III类和IV类标准时,入湖总磷负荷阈值分别为2.1和2.6 mg P m^-2 d^-1。在建设用地快速增长情景下,若使白洋淀水质达到III类标准,入湖总磷负荷应减少131 t。     

Multivariate analysis of heavy metal and nutrient concentrations in sediments of Taihu Lake, China*

Taihu Lake is one of the largest freshwater lakes in China. The Lake is very shallow with a mean depth of 1.9 m and an area of 2428 km². Nutrient concentrations (Org-C, Tot-N and Tot-P) and heavy metal concentrations (Ag, As, Cd, Co, Cr, Cu, Hg, Ni, Pb, Sr, Zn, etc.) in the lake's surface sediments were sampled at 13 locations. This was done to determine if industrialized areas along the lake's coastline were impacting the nutrient and heavy metal distribution of the lake's surface sediments. Principal Component Analysis (PCA) was used to assess the degree of contamination and spatial distribution of heavy metals and nutrients in different areas of Taihu Lake.A distinctive spatial distribution of heavy metals and nutrients was observed. Sediments from a large embayment of Taihu Lake called Lake Wulihu had significantly higher nutrient concentrations (Org-C, 2.05–3.83%; Tot-N, 0.28–0.54%; Tot-P, 0.10–0.33%) than any other area of Taihu Lake. These high nutrient levels were associated with the input of untreated domestic sewage from the large (circa one million people) City of Wuxi, which discharges its effluents into the Liangxi River. As a result, Lake Wulihu is the most eutrophic area of Taihu Lake. The nearby Meiliang Bay suffered from the worst heavy metal contamination in Taihu Lake (e.g. As, 64.0; Ag, 4.2; Cd, 0.93; Co, 14.2; Cr, 155.0; Cu, 144.0; Hg, 0.25; Ni, 79.8; Pb, 143.0 and Zn, 471 mg kg^–1). These high heavy metal concentrations were ascribed to the discharge of untreated and partially treated industrial waste water from Changzhou and Wujin via the Zhihugang River. Surface sediment samples from the east basin of Taihu Lake were characterized by high Org-C (1.0–2.3%) and Tot-N (0.18–0.37%) and low Tot-P (0.048–0.056%) concentrations. It is likely that macrophytes removal accounts for a major reduction of phosphorus in the sediments of the east basin of Taihu Lake.     

Evaluation of recent limnological changes at Lake Apopka

Recent changes in submersed macrophytes and water quality variables have been offered as the strongest evidence that the current restoration program at Lake Apopka will be effective (Lowe et al., 2000); however, the new beds of submersed plants in Lake Apopka are found only on hard substrates on the fringes of the lake within 40 m of shore and are protected from waves by cattails (Typha spp.). They occupy only 0.02% of the lake area, and there is no indication that they can colonize the flocculent sediments that make up 90% of the lake area. There is no correlation between annual inputs of phosphorus and total phosphorus concentrations in the lake, and patterns of change in chlorophyll and other water quality variables do not follow changes in phosphorus loads. Rather than reflecting decreases in phosphorus loading, the recent changes could be related to the harvest of benthivorous fish or are just the normal fluctuations found in lakes that have not been perturbed. Regardless of the reason the macrophytes were lost in the 1940s, the new analyses confirm our previous findings that the high turbidities in Lake Apopka are due to the resuspension of sediments, and that the fluid mud cannot support the colonization of submersed aquatic macrophytes. Even without the fluid mud, the target phosphorus concentration of 55 mg m^–3 is too high to bring about the restoration of the former macrophyte beds in the lake.     

Seasonal Dynamics of Picocyanobacteria and Picoeukaryotes in a Large Shallow Lake (Lake Balaton,Hungary)

The abundance and composition of autotrophic picoplankton (APP) were studied between February 2003 and March 2004 in Lake Balaton. Water samples were taken fortnightly in the eutrophic western basin and mesotrophic eastern basin. Our study, which took more than one year, revealed pronounced seasonal pattern of the picoplankton abundance and composition. According to our results there were three types of picoplankton in Lake Balaton: 1. Phycoerythrin‐rich coccoid cyanobacteria (PE), dominant summer picoplankters in the mesotrophic lake area; 2. Phycocyanin‐rich cyanobacteria (PC), the most abundant summer picoplankters in the eutrophic lake area; 3. Picoeukaryotes, dominant winter picoplankters in the whole lake. The observed abundance of picoeukaryotes (3 × 10⁵ cells ml^–1) was one of the highest ever found. Our study confirms that in Lake Balaton the colonial autotrophic picoplankton (colonial APP) become dominant in summer in the nutrient limited period. We have found strong negative relationship between the concentrations of available nitrogen forms (NH₄–N, NO₃–N, urea‐N) and the colonial APP abundance. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Role of Fish Communities in Water Quality Management of a Large Shallow Lake

Management measures of Lake Balaton such as wetland reconstruction at the main inflow to the lake along with the “unplanned” commercial fishery led to great changes in the density and biomass of fish populations. There was no significant difference in CPUE data between the two, eastern and western, basins. Biomass of total fish stock in Lake Balaton has decreased substantially, 2–3 times between 1991–1999, and ranges between 120–194 kg ha⁻¹. Bottom‐up effects are more important than the top‐down effects due to the impact of internal nutrient load. Changes in the biomass and thus the activity of omnivorous fish in the lake lowered the intensity of various indirect effects and feedback mechanisms causing changes in the nutrient metabolism of the lake. Intensified fishery effort in Lake Balaton did not result in an increased stock of piscivores. The ratio of piscivores and omnivores remained at 5% during the whole study period. Despite this low piscivores to omnivores ratio, the water quality has improved in all basins.     

Nutrient retention by the Kis-Balaton Water Protection System

Water quality of Lake Balaton, particularly that of its south-western basin (the Keszthely-Bay), has been deteriorating faster and faster. The greatest transporter of inorganic nutrients to the Bay is the Zala River.The lower valley of the river was part of the lake until about 200 years ago. Later, a large part of the area was turned to a wetland, while the smaller part dried up.To retain the nutrients from Keszthely-Bay, the former marshland is now being reconstructed: the so-called Kis-Balaton Water Protection System (KBWPS). The first part of the System, the Hidvégi-Pond, has been operating since the middle of 1985. The second stage, the Fenéki-Pond, to be finished by the end of this century, is now under construction. The main purpose of the KBWPS is to gain enough time to build up the technology necessary for an adequate protection of Lake Balaton.From the beginning of the operation of the Hidvégi-Pond a multidisciplinary research program has been carried out to monitor the hydrological, hydraulical, ecological, and biological processes in the reservoir. This program focused on nitrogen and phosphorus loadings and retention. Input and output loads were estimated from daily measurements. The mechanisms of retention were studied in special projects.With the exception of TN, nutrient retention increased from year to year. In 1990, 96% of PO₄-P, 87% NO₃-N, and 58% of TP were retained.This efficiency exceeds expectations. Retention of TN is the lowest (about 20%), due to N₂-fixation by blue-green algae. However, the second stage needs to be implemented, since there is an additional external load from the watershed of the lower valley, and nutrient release takes place during decomposition of the organic matter which leaves the Hidvégi-Pond.     

沉水植物重建对富营养水体氮磷营养水平的影响

利用富营养浅水湖泊(武汉东湖)中所建立的大型实验围隔系统,研究了沉水植物对水体N、P营养水平的影响．结果表明,沉水植物重建后N、P营养水平显著降低．在研究期间,水生植物围隔总N和总P水平均显著低于对照围隔和大湖水体,而且水生植物围隔的总P含量一般维持在0．1mg·L^-1左右。季节性波动远低于对照围隔和大湖水体．水生植物围隔水体中氨态氮和亚硝态氮含量较低．而硝态氮含量与对照围隔和和大湖水体差别不大．由此可见。恢复以沉水植物为主的水生植被,可以有效地降低N、P营养循环速度,控制浮游植物过度增长,是重建富营养湖泊生态系统的重要措施．     

Nutrient dynamics linked to hydrological condition and anthropogenic nutrient loading in Chaohu Lake (southeast China)

Chaohu Lake, a large (770 km²) shallow lake in the Yangtze River basin, has experienced serious eutrophication over the past three decades. To track its nutrient history and the causes, multi-proxies (diatom, geochemical indicators, magnetic susceptibility, and grain size) were analyzed on a 120-cm long core from the lake. Nutrient dynamics of the past 500 years were reconstructed using sedimentary diatom assemblages and an established diatom-inferred total phosphorus (DI-TP) transfer function. Between about 1500 and 1740 AD, the lake remained in an upper-mesotrophic state with the DI-TP oscillating around 60 ??g l^?1. Together with enhanced agricultural activities, a drier and warmer climate led to a decrease in water level and water exchange volume with the Yangtze River, thus triggering the first phase of eutrophication (ca. 1740?C1820 AD). After this eutrophic episode, the lake had exhibited a recovery in nutrient status until the 1960s. However, the lake became susceptible to nutrient input due to a sharp decrease in water exchange volume after its impoundment in 1962. A large amount of anthropogenic nutrient input has exacerbated eutrophication in the lake since the late 1970s. Redundancy analysis using a range of sedimentary proxies indicated that the two eutrophication phases were mainly attributed to anthropogenic nutrient loading and altered hydrological conditions. The hydraulic connection with the Yangtze River should be the primary self-adjustment mechanism of the lake against anthropogenic nutrient input.     

Modelling nutrient cycles in relation to food web structure in a biomanipulated shallow lake

The modelPCLAKE describes the phosphorus and nitrogen cycles within a shallow lake ecosystem, including the sediment and a simplified biological food web. All components are modelled in a generalized way rather than a very detailed one. This model has been applied to Lake Zwemlust, a small biomanipulated lake in The Netherlands. Formerly, this highly eutrophic lake was dominated by cyanobacteria and devoid of macrophytes. Biomanipulation was carried out in 1987 by pumping-out of the water, removal of all fish, and refilling of the lake with seepage water. The lake was restocked with some rudd, pike, zooplankton and seedlings of macrophytes, and then monitored up to 1992. Macrophytes developed rather quickly and reached their maximum biomass during the six-years period in 1989. Despite the continuously high nutrient (N and P) loading, algal biomass remained low due to nitrogen limitation, caused by competition with the macrophytes. From 1990 onwards, the macrophytes declined again and a species shift occurred, following an increase of herbivorous birds on the lake and the development of herbivorous fishes.Model simulations grossly reproduced the observed developments in Lake Zwemlust before and after the biomanipulation measures. The existence of multiple steady states at the same trophic state and the possible shift between them could be simulated well. This study also demonstrates the interrelation between system structure and the distribution and cycling of nutrients. It is concluded, that within general boundary conditions set by the trophic state of the system, the food web structure determines the actual nutrient flows and the occurrence of nutrient limitations of the primary producers. It is shown that both aspects can be integrated in one mathematical model. The long-term stability of the macrophyte dominance in the lake is discussed.     

The cycling of nutrients in a closed-basin antarctic lake: Lake Vanda

Lake Vanda is a permanently ice covered, meromictic, closed basin lake, located in the Dry Valley region of Southern Victoria Land, Antarctica. A unique feature of the lake water column structure is that the bottom lake waters exist as a natural diffusion cell. The diffusive nature of these waters allows rates of sulfate reduction, nitrification and denitrification to be calculated from nutrient concentration gradients. Calculation reveals that sulfate reduction is by far the most important anoxic process acting to oxidize organic material. In addition, rate calculations reveal that bottom water nutrient profiles are in steady state. One argument in support of this conclusion is that the calculated rate of nitrification balances the flux of ammonia from the anoxic lake waters. The flux of phosphorus from the reducing waters is several times less than would be predicted from the nitrogen and phosphorus content of decomposing lake seston. Solubility calculations show that phosphorus may be actively removed at depth in Lake Vanda by the formation of hydroxyapatite. It is found that estimated rates of nitrogen and phosphorus removal in the bottom lake waters and sediments roughly balance the riverine input flux. This suggests that throughout the lake a nutrient steady state may exist, and that the anoxic zone may be the most important loci for nutrient removal. Finally, the ratio of nitrogen to phosphorus entering Lake Vanda by riverine input is less than the Redfield ratio of 16/1; in contrast to the lake waters which are strongly phosphorus limited at all depths. This curious aspect of the lake's nutrient chemistry is explained by the presence of preformed nitrogen, which has been concentrated in the deep brine due to several episodes of evaporative concentration.     

Biomass Allocation in Cyperus papyrus in a Tropical Wetland,Lake Naivasha,Kenya1

The nutrient status of Lake Naivasha, a freshwater lake in southeastern Kenya, has been rising since at least 1982. A potential effect of increases in nutrient supply to the lake's floating papyrus is increasing of the plants’ investment in above–water material and reduction of the amount of energy invested in uptake and storage. Biomass and its allocation between culms, panicles, roots, and rhizomes was measured in 17 sites around the 150–km² lake. Although above–water biomass was greatest in sites closest to the lake's major nutrient inflow, the River Malewa, there was little evidence of corresponding decreases in the biomass of uptake and storage tissues. In August 1995, the average ± SD biomass of papyrus in the lake was 11,540 ± 3020 g/m², with the papyrus containing about 4500 ± 1900 g total carbon/m² and about 100 ± 70 g total nitrogen/m². Plant nitrogen contents did not vary with distance from the main external nutrient supply. Together with low nitrogen concentrations in the plants (0.60 ± 0.26 in culms and 0.99 ± 0.50% in rhizomes), very high carbon to nitrogen ratios (49 ± 20:1) and nitrogen fixation in the rhizosphere explaining only about half of the plants’ nitrogen, papyrus is a likely net sink for nitrogen supplied from the lake's increasingly cultivated watershed. Despite this role, clearance of papyrus in favor of agriculture partly explains the reductions in the area of papyrus within the lake basin from 48 km² in the late 1960s to 14 km² in 1995.     

近33年白洋淀景观动态变化

湿地具有重要的生态功能,由于各种因素的影响改变了湿地水文条件,并且导致湿地退化。利用1974、1987、1996和2007年遥感影像,使用ERDAS 9.1、ARCGIS 9.2和FRAGSTATS 3.3,分析了白洋淀景观动态变化过程及其驱动力。研究结果表明:从1974至2007年,白洋淀湿地面积从249.4km²下降到182.6km²,农田和居民地面积分别从70.0、2.1km²增加到126.4、12.5km²;在景观水平上,斑块密度、景观形状指数和香农多样性指数增加,蔓延度减小,景观破碎化程度增加,优势景观类型湿地对整个景观的控制作用减小;在类型水平上,明水面和沼泽的斑块密度和周长-面积分维数增加,最大斑块指数、平均斑块面积和连接度减小,居民地的斑块密度、最大斑块指数、平均斑块面积、周长-面积分维数和连接度都增加,农田的斑块密度、最大斑块指数和连接度增加,平均斑块面积和周长-面积分维数减小;水位变化是影响白洋淀景观变化的主要因素,水位升高会使湿地面积增加,反之,使湿地面积减小;流域人类活动和降水量变化是白洋淀水位和景观变化的重要驱动力。引水补淀只能暂时缓解白洋淀缺水问题,从流域角度考虑,实施有效的水资源管理方式,才能从根本上解决白洋淀湿地退化的问题。     

Short-term and long-term effects of zooplanktivorous fish removal in a shallow lake: a synthesis of 15 years of data from Lake Zwemlust

SUMMARY 1. Removal of zooplanktivorous fish (mainly bream) in 1987 from a shallow eutrophic lake in the Netherlands, Lake Zwemlust, resulted in a quick switch from a turbid state with cyanobacteria blooms to a clear state dominated by macrophytes.
2. The clear state was not stable in the long term, however, because of high nutrient loadings.
3. In 1999, another removal of zooplanktivorous fish (mainly rudd) had similar effects as in 1987, although macrophytes returned more slowly.
4. In the years directly following both interventions there was a 'transition period' of very clear water with high densities of zooplanktonic grazers in the absence of macrophytes; low oxygen concentrations indicate that during those years primary production was low relative to heterotrophic activity.
5. The transition period appears to provide the light climate necessary for the return of macrophytes.
6. Reduction of nutrient loading is necessary to improve water quality in Lake Zwemlust in the long term. In the short term, repeated fish stock reduction is a reasonable management strategy to keep Lake Zwemlust clear.     

An assessment of the importance of emergent and floating-leaved macrophytes to trophic status in the Loosdrecht lakes (The Netherlands)

The potential importance of the six major emergent and floating-leaved macrophyte species in recycling of sediment phosphorus in the Loosdrecht lakes was studied. Representative plant samples were collected at the time of maximum biomass, and analysed for biomass and carbon, nitrogen and phosphorus contents. Species cover was determined by aerial photography.Total cover in the seven lakes studied ranged between 2 and 26 percent. For the four main species, biomass per unit area increased with lake trophic status. Consistent differences in C, N and P contents per unit biomass were not observed. Although cover values were small, significant amounts of C, N and P were contained in the macrophytes when compared with maximum sestonic content.Potential P loads from macrophyte decay were calculated. In Lake Loosdrecht, the P load represented 15 percent of current external P inputs. The potential importance of macrophyte decay to P recycling in the other lakes is greater.Decay of macrophyte species at the end of the growing season appears to affect autumnal nutrient and chlorophyll a levels in the water column of some lakes. The re-establishment of submerged species following lake restoration may increase the importance of this pathway in the lakes.     

Experiments on Nitrogen and Phosphorus Release by Chironomus ex gr. plumosus from the Sediments of Lake Balaton,Hungary

Sediment-water systems of Lake Balaton mud and tap water were constructed in plexiglass tubes and boxes for evaluation of changes in the nitrogen and phosphorus contents of overlying water as influenced by chironomid density and light conditions. Nitrogen flux from sediment was greatly influenced by denitrification process. The amount of TN released by chironomids amounted to about half of the yearly nitrogen fixation rate in Lake Balaton. Omnivorous chironomids increased the phosphorus content of the overlying water. The rate of release was density dependent. TP release rates ranged between 1–17 mg m⁻² day ⁻¹ over a range of densities 500–20,000 larvae m⁻². It became evident that aerobic sediment cores can be an important nutrient source in lakes where chironomids inhabit them at densities above 1,000 larvae m⁻².     

Fish manipulation as a lake restoration tool in shallow,eutrophic temperate lakes 1: cross-analysis of three Danish case-studies

The use of fish manipulation as a tool for lake restoration in eutrophic lakes has been investigated since 1986 in three shallow, eutrophic Danish lakes. The lakes differ with respect to nutrient loading and nutrient levels (130–1000 μg P l⁻¹, 1–6 mg N l⁻¹). A 50% removal of planktivorous fish in the less eutrophic cyanobacteria-diatom dominated Lake V?ng caused marked changes in lower trophic levels, phosphorus concentration and transparency. Only minor changes occurred after a 78% removal of planktivorous fish in eutrophic cyanobacteria dominated Frederiksborg Castle Lake. In the hypertrophic, green algae dominated Lake S?byg?rd a low recruitment of all fish species and a 16% removal of fish biomass created substantial changes in trophic structure, but no decrease in phosphorus concentration. The different response pattern is interpreted as (1) a difference in density and persistence of bloomforming cyanobacteria caused by between-lake variations in nutrient levels and probably also mixing- and flushing rates, (2) a difference in specific loss rates through sedimentation of the algal community prevaling after the fish manipulation, (3) a decreased impact of planktivorous fish with increasing mean depth and (4) a lake specific difference in ability to create a self-increasing reduction in the phosphorus level in the lake water. This in turn seems related to the phosphorus loading.     

Trophic status of Tilitso,a high altitude Himalayan lake

The trophic status and water quality of Lake Tilitso (4920 m above sea level) in a high altitude region in central Nepal were surveyed in September, 1984. The lake is rather large with a maximum depth of 95 m and a surface area of 10.2 km². The lake water was turbid due to glacier silt and the euphotic layer was only 5 m deep. The nutrient concentration was very low with total phosphorus concentration 1–6 μg l⁻¹, and DTN concentration 0.10–0.22 mg l⁻¹. The phytoplankton biomass and chlorophyll-a concentration were also low. Primary production was estimated to be about 12 mg C m⁻² d⁻¹. The concentrations of particulate matter and most cations and bacterial number were higher in the epilimnion than in the hypolimnion. The trophic status of this lake was estimated as ultraoligotrophic.     

Echosounding observations of coverage,height, PVI,and biomass of submerged macrophytes in the southern basin of Lake Biwa,Japan

We have developed a procedure to process echosounding data to map the distribution of submerged aquatic macrophytes in the southern basin of Lake Biwa, a water body that has a surface area of 52 km² and a mean depth of 4 m. Echosounding observations were made along 27 transect lines spaced at 500-m intervals on August 4 and September 2 and 30, 2003. Quantitative vegetation data including percent coverage, mean vegetation height, and percent vegetation infestation were directly determined using image data from the echosounder recorded digitally on videotape. Based on the image data from an echosounder, a regression model was developed for estimating biomass of submerged macrophytes. The regression model using the total echo strength as the explanatory variable could reliably estimate macrophyte biomass up to 300 g m⁻². Distribution maps of macrophyte height and biomass suggest that the recent summer decline of submerged macrophytes started earlier in shallow areas (<3 m of depth) than deep areas (>4 m) in the southern basin of Lake Biwa.     

Rehabilitation and management of a moderately deep-stratifying reservoir by the use of nutrient reduction and food-web management

As expected from its short renewal time, the hypertrophic Lingese Reservoir responded rapidly but incompletely to external nutrient reduction in 1993. Although there was a sudden decline in lake phosphorus and chlorophyll concentrations, the ‘turbid regime’ revealed resistance in this weakly stratified reservoir of intermediate depth. Draining the reservoir in autumn 1995 provided an unprecedented opportunity for sediment treatment—the phosphorus-rich surface layer was inverted and covered with deeper nutrient-poor layers—and removal of the dense cyprinid fish stock which had not responded to sewage diversion, at least in the short term. Commencing with refilling in 1999, a new fish stock was built up from 2000 by only stocking predators (fingerlings of pike, pike-perch and larger specimens of rainbow-trout in the first years) in combination with catch restrictions. Concomitantly, with the appearance of daphnids in 1999, a ‘clear water regime’ was established and lake water phosphorus concentrations decreased at unchanged external loading. Reduced zooplanktivory as well as reduced fish-mediated phosphorus release from the sediments were driving mechanisms behind successful reduction of internal loading and achievement of a ‘clear water regime’. Hence, phosphorus concentrations were revealed to be a response variable not only to input management but also to food-web management. As the development of cyprinid dominance was prevented in the long-term, there is ample evidence that the fish community responded to the applied management measures as expected featuring successful food-web management. Overall, the biological structure was revealed to be of major importance for lake phosphorus availability and turbidity as in shallow lakes, without, however, the establishment of macrophyte dominance.     

Nitrogen and phosphorus dynamics and retention in ecotones of Lake Titicaca,Bolivia/Peru

We are studying present conditions and consequences of material movement from land to water in the Lake Titicaca basin, and how fluxes are affected by human activities. The principal objective of this research is to describe and explain the variability in the Andean Altiplano of (a) water, nutrient and sediment fluxes from land and (b) composition, nutrient limitation and other important features of nearshore lake communities, and compare the effects of different agricultural practices (especially traditional and modern) on these factors. We are focusing on a comparison of the impacts of two forms of agriculture in this region: ancient raised fields currently under rehabilitation, and flat pastures and fields, which are more common. Results of the first year of study indicate there is substantial variability in nitrogen and phosphorus dynamics in relation to ecotone complexity (simple vs. intermediate vs. complex). Raised field sites have the beneficial effect of reducing high available nutrient concentrations (nitrate and soluble reactive phosphorus) and sediment load (measured as turbidity) as the water passes through them enroute to the lake. Aquatic vegetation (algae and macrophytes) reflect well ambient total nitrogen and phosphorus concentrations. Experimental nutrient limitation bioassays indicate that nitrogen is the most important limiting nutrient, though there is important spatial variability within the landscape, and phosphorus as well as nitrogen can be limiting.