Macrozoobenthos of Lake Peipsi-Pihkva: long-term biomass changes

Macrozoobenthos of the large (3,558 km²) Lake Peipsi-Pihkva was monitored at 22–24 sampling spots yearly in June 1964–1994 as well as 50 shallow-water profiles in mid-summer 1970, 1980, and 1990. No qualitative changes were observed in the bottom fauna, except for the introduction of a Baikalian gammarid species, Gmelinoides fasciatus. The average total biomass in June (without big molluscs) revealed considerable annual fluctuations, with an insignificant general tendency of increase. The increase was significant in the biomass of several Mollusca (including the highly abundant big clam Dreissena polymorpha), Asellus, Gammaridae, and Hirudinea but not in the most abundant animal groups Chironomidae and Oligochaeta. The low biomass of Ephemeroptera and Hydrachnellae decreased significantly. The mid-summer samples taken from the shallow-water zone in three different years revealed the highest biomass in 1980 and the lowest in 1990 (the latter being probably related to the high water level). A gradual decrease in the biomass of the Ephemeroptera and Hydrachnellae as well as the Oligochaeta, Pisidiidae and Bithynia tentaculata occurred in the shallow-water zone, while the Gammaridae increased on the account of the introduced species. No coincidence was found with the neighbouring Lake Võrtsjärv when comparing the annual fluctuations of biomass. A general tendency to a slow increase in total biomass and a decrease in the biomass of the most vulnerable groups Ephemeroptera and Hydrachnellae, probably due to progressing eutrophication, were common for both lakes.     

Distribution of Sediment Phosphorus Fractions in Hypertrophic Strongly Stratified Lake Verevi

Lake Verevi is a hypertrophic and strongly stratified (partly meromictic) small temperate lake. Vertical distribution of sediment phosphorus fractions as well as iron, manganese, organic matter and calcium carbonate of the deep bottom sediment was determined. The study focused on the ecologically important layer of the sediment [<20(45) cm]. In the uppermost layers of the sediment, NaOH-NRP (organic P) dominated while HCl-RP (apatite-P) became dominant in some deeper layers below 7 cm. Extremely high concentrations of labile phosphorus fraction (NH₄Cl-RP) indicated the low binding capacity of phosphorus by lake sediment. Due to sediment and hypolimnion anoxia, the internal load of phosphorus in this lake is most likely. Potentially mobile phosphorus fractions (NH₄Cl-RP, BD-RP, NaOH-NRP) formed 301 kg in upper 10 cm thick sediment layer of hypolimnetic bottom sediment (40% of lake bottom area).     

Optical Properties and Light Climate in Lake Verevi

The optical properties and light climate during the ice-free period in the highly stratified Lake Verevi (Estonia) have been studied together with other lakes in same region since 1994. The upper water layer above the thermocline belongs to class “moderate” by optical classification of Estonian lakes but can turn “turbid” (concentration of chlorophyll a up to 73 mg m⁻³ and total suspended matter up to 13.2 g m⁻³) during late summer blooms. In the blue part of the spectrum, light is mainly attenuated by dissolved organic matter and in red part notably scattering but also absorption by phytoplanktonic pigments effect the spectral distribution of underwater light. Consequently, the underwater light is of greenish-yellow color (550–650 nm). Rapid change in optical properties occurs with an increase of all optically active substances close to thermocline (2.5–6 m). Optical measurements are often hampered beneath this layer so that modeling of the depth distribution of the diffuse attenuation coefficient is an useful compliment to field measurements. K_d,PAR ranges from 0.8 to 2.9 m⁻¹ in the surface layer, and model results suggest that it may be up to 5.8 m⁻¹ in the optically dense layer. This forms a barrier for light penetration into the hypolimnion.     

Water and Nutrient Mass Balance of the Partly Meromictic Temperate Lake Verevi

Mass balances of total nitrogen and total phosphorus were calculated for Lake Verevi (area 0.126 km², maximum depth 11 m, mean depth 3.6 m), a sharply stratified small lake located in South Estonia within the borders of the town Elva. The lake has up to 10 small inflows but only three of them are nearly permanent. Accidental overflows from near-by oxidation ponds during high floods have been the major source of the nutrient load of the lake in the past. L. Verevi receives a significant part of its inflow from groundwater, which is difficult to measure. In dry years the outflow is temporary. During summer the lake is sharply thermally and chemically stratified. The spring turnover is often incomplete even in homothermal conditions, thus giving the lake some meromictic features. The influx of nitrogen exceeded the outflux at any supposed proportion (20%, 50%, 80%) of surface runoff. The lake retained 45–90% of the nitrogen influx by sedimentation and/or by denitrification. The largest nitrogen losses with loss rates more than 10 kg N d⁻¹ occurred in May and June. The calculated phosphorus retention rate became strongly negative during mixing periods. From June to November, phosphorus release from the sediment exceeded sedimentation by 205 kg in 1991 and by 79 kg in 1993. Earlier stagnation and absence of a full spring turnover in the 2000 has slowed down the recovery of the lake because less phosphorus is flushed out. However, the stronger stratification and significantly smaller phosphorus content in the epilimnion limits biological activity and as a result improves the water quality of the surface layer.     

Impact of Macrozoobenthos on Two-Dimensional Small-Scale Heterogeneity of Pore Water Phosphorus Concentrations: <Emphasis Type="Italic">in-situ</Emphasis> Study in Lake Arendsee (Germany)

An in-situ study was conducted in Lake Arendsee to study the influence of macrozoobenthos on pore water phosphate concentrations, and to investigate the importance of macrozoobenthos in causing small-scale heterogeneity. Two-dimensional pore water samplers with a high spatial resolution were exposed for 14 days at two sampling points with different water depths. Macrozoobenthos densities and the corresponding pore water phosphate concentrations were determined. In profundal sediments with chironomids (mean density: 480 m⁻²) the pore water phosphate concentration showed more patchiness (heterogeneity index 0.69) than in sediments without chironomids (heterogeneity index 0.38). Macrozoobenthos might affect the sediment environment mainly through bioirrigation, bioturbation, secretion, and digestion. It is most likely that the hot spots are caused by secretions from chironomids which intensify the microbially mediated P-release. The small-scale horizontal heterogeneity of pore water concentrations due to macrozoobenthos activities is insufficiently considered in many limnological studies focusing on vertical changes of pore water concentrations to investigate biogeochemical processes in sediment and to estimate internal nutrient loading. In sediments inhabited by macrozoobenthos the number of replicates should be high due to the extreme variability of single profiles of the two-dimensional sampler, as well as of averaged profiles simulating classical one-dimensional pore water analysis techniques. In cases where the profundal sediment is macrozoobenthos-free, single deployments of one-dimensional pore water samplers are well suited to describing pore water chemistry. Thus, determination of macrozoobenthos density is essential for study design.     

Nitrogen Dynamics in the Steeply Stratified,Temperate Lake Verevi,Estonia

The dynamics of different nitrogen compounds and nitrification in diverse habitats of a stratified Lake Verevi (Estonia) was investigated in 2000–2001. Also planktonic N₂-fixation (N₂fix) was measured in August of the observed years. The nitrogen that accumulated in the hypolimnion was trapped in the non-mixed layer during most of the vegetation period causing a concentration of an order of magnitude higher than in the epilimnion. The ammonium level remained low in the epilimnion (maximum 577 mgN m⁻³, average 115 mgN m⁻³) in spite of high concentrations in the hypolimnion (maximum 12223 mgN m⁻³, average 4807 mgN m⁻³). The concentrations of NO₂⁻ and NO₃⁻ remained on a low level both in the epilimnion (average 0.94 and 9.09 mgN m⁻³, respectively) and hypolimnion (average 0.47 and 5.05 mgN m⁻³, respectively). N₂fix and nitrification ranged from 0.30 to 2.80 mgN m⁻³ day⁻¹ and 6.0 to 107 mgN m⁻³ day⁻¹, respectively; the most intensive processes occurred in 07.08.00 at depths of 2 and 5 m, accordingly. The role of N₂fix in the total nitrogen budget of Lake Verevi (in August 2000 and 2001) was negligible while episodically in the nitrogen-depleted epilimnion the N₂fix could substantially contribute to the pool of mineral nitrogen. Nitrification was unable to influence nitrogen dynamics in the epilimnion while some temporary coupling with ammonium dynamics in the hypolimnion was documented.     

Macrozoobenthos of Lake Peipsi-Pihkva: taxonomical composition, abundance, biomass, and their relations to some ecological parameters

The large but shallow (3,558 km², up to 15.3 m deep) lake is eutrophic, with Chironomus plumosus and Potamothrix hammoniensis as dominating macroinvertebrates in the profundal. The extensive well-aerated sublittoral with sandy bottom sediments has a mesotrophic appearance and supports a diverse fauna with several oxyphilous species, including a very abundant population of Dreissena polymorpha. The phytophilous fauna is limited to small sheltered areas only. The average abundance of the small animals of macrozoobenthos (without big molluscs) was 2,617 ind. m^–2, their biomass 12.34 g m^–2 (corresponding to 52.2 kJ m^–2) in 1964–1994. The same figures for big molluscs (mostly Dreissena) were 304 ind. m^–2 and 238 g m^–2 in 1964–1994, and even 864 ind. m^–2 and 687 g m^–2 in 1985–1988, at the time of their special mapping. The sublittoral zone revealed the lowest biomass of small animals but the highest biomass of big molluscs. The southern, shallower lake regions, more enriched with nutrients and better protected from wind, revealed a significantly higher biomass of small macrozoobenthos in the near-shore zone than the cleaner and open northern part, while no positive effect of enrichment was observed neither in the biomass of profundal zoobenthos nor in that of big molluscs. The production of the small macrozoobenthos was calculated as 111 and 53 kJ m^–2 during two annual cycles in Lake Peipsi s. s., the most productive period being the autumn overturn. Lake Peipsi-Pihkva has the highest abundance and biomass of macrozoobenthos among the large lakes of North Europe.     

The Formation and Dynamics of Deep Bacteriochlorophyll Maximum in the Temperate and Partly Meromictic Lake Verevi

Vertical distribution of phytoplankton and the formation of deep chlorophyll maximum (DCM) in the metalimnion of a small stratified and partly meromictic temperate lake was studied in 1999 and 2000. During summer DCM usually occurred on the borderline of H₂S and oxygen-containing waters. At the depths where the bacteriochlorophyll (Bchl) maxima were observed, the sulphide concentration was usually relatively low compared to the bottom layers, where its concentration reached as high as possible saturation level. In April 2000, DCM was formed at the depth of 3.5 m, and lowered thereafter slowly to 6.5 m by October. The concentration of Bchl d reached the highest values (over 1000 μg l⁻¹) just before the water column was mixed up in autumn. In December and April Bchl d was detectable only near the bottom of the lake. The concentration of chlorophyll a yielded by the spectrophotometric phaeopigment corrected method and by HPLC (high pressure liquid chromatography), fit rather well in the upper layers. In deeper water layers chlorophyll a concentration (Chl a) measured by spectrophotometry was overestimated about 47 times if compared to HPLC values because of the high Bchl d in that layer. In most cases vertical profiles of primary production (PP) did not coincide with the vertical distribution of the pigment content; the maximum values of PP were found in the epilimnion. In some cases PP had notably high values also at the depth of DCM. In the upper layers Chl a usually did not exceeded 20 μg l⁻¹ in spring and 10 μg l⁻¹ in summer_. The moderately high Chl a in the epilimnion in spring was significantly reduced after the formation of thermocline most probably because of the establishment of the nutrient limitation in epilimnion. Decreasing Chl a concentration in the epilimnion led to increased water transparency and better light conditions for photosynthetic bacteria in metalimnion.     

An instance of thermal instability in Lake Simbi,Kenya

In July and August, 1985, saline Lake Simbi (Kenya) had a strong chemocline in the upper 4 meters and a pronounced cool layer (24.6–25.2 °C) at 2.5 m depth lying above a slightly warmer layer. Rainfall, spring inflows and nocturnal cooling are suggested as responsible for the low temperatures in the upper warm column.     

Macrozoobenthos of three Pennsylvania lakes: responses to acidification

The littoral macrozoobenthos (MZB) of three northeastern Pennsylvania lakes was sampled seasonally from summer 1981 until summer 1983, to determine if any changes were occurring in response to acid deposition. In the acidified lake (total alkalinity 0.0 eq L^–1) the mean pH decreased from 5.5 in 1981 to 4.2 in 1983. Chironomidae comprised 71.30% of the MZB numbers and 19.6% of the wet weight. Over the study period the wet weight of Chironomidae increased (p < 0.04) as did the total numbers of Chironomidae in general (p < 0.01) and Tanytarsini (p < 0.01) in particular. Total numbers of MZB also increased (p < 0.02) in the acidified lake, but there was no significant change in the number of taxa, diversity or total wet weight. In the moderately sensitive lake (total alkalinity 47.4 eq L^–1, mean pH 6.1) Chironomidae were numerically (43%) dominant but Odonata (18.6%) and Mollusca (12.7%) dominated wet weight. There were no significant changes in the MZB of the moderately sensitive lake over the study period. In the least sensitive lake (total alkalinity 190 eq L^–1, mean pH 6.6) the Amphipoda (31.3%) and Chironomidae (27.3%) together provided 58.6% of the MZB numbers, and the Mollusca formed 55.1% of wet weight. Wet weight at the least sensitive lake was higher (p < 0.01) and there were more Ephemeroptera, Pelecypoda and Gastropoda than at the other two lakes. There were no differences in total numbers, diversity or number of taxa among the three lakes.     

胶州湾西北部潮滩湿地大型底栖动物功能群

2009年2、5、8和11月进行了7个断面35个站位的大型底栖动物调查,选取高潮区(A)、中潮区(B、C、D)和低潮区(E)研究了胶州湾西北部潮滩湿地大型底栖动物功能群组成及其时空变化.调查共发现大型底栖动物71种,主要种类为软体动物(31种)、环节动物(20种)和节肢动物(14种).潮区A、B、C、D、E物种数分别为26、33、35、38、31.依据食性将主要底栖动物划分为肉食者、浮游生物食者、碎屑食者和杂食者4个功能群.各功能群物种数占总物种数的百分比由高到低依次是肉食者、浮游生物食者、碎屑食者和杂食者.各功能群中肉食者的多样性指数最高,杂食者最低.各功能群的丰度、均匀度指数、多样性指数一般都是中潮区较高,高潮区和低潮区较低.大型底栖动物功能群的分布随潮区环境的改变而变化,是对生境状况的综合反映.     

Sedimentation Rate of Seston during the Formation of Temperature Stratification after Ice Break-up in the Partly Meromictic Lake Verevi

The small strongly stratified hard-water hypertrophic lake Verevi (max. depth 11.0 m, surface area 12.6 ha, mean depth 3.6 m) was investigated in 2000 and in 2001. The lake is sheltered from winds, and the role of waves in mixing the water column is minimal. Eutrophication favours the strengthening of stratification. Early warm springs cause a fast stagnation of the water column forming partly meromictic conditions. Seston content of water and in sediment traps in 3 layers was measured several times during the formation of stratification. Besides measuring particulate matter, in 2001, the nutrient content of the trapped sediment was analysed. During the first 7 days of the investigation, 30% of the total particle sedimentation took place. The sedimentation rate of particulate matter was 0.4–6.3 g m^–2 d⁻¹ dry weight in different layers of the water column. Daily average sedimentation loss rate was 27% of the total amount of seston of the epilimnion, whilst from the meta- and hypolimnion the settling was much slower (9.6 and 7.3%, respectively). In our experiments with twin sediment traps, to one of which formaldehyde was added, the PO₄³⁻-P concentration was 19% smaller in the trap without formaldehyde, probably due to planktonic uptake. The relationship between primary and export production is loop-like. The shape was irregular, indicating a high grazing rate of zooplankton.     

Influence of the Thin Drift Algal Mats on the Distribution of Macrozoobenthos in Kõiguste Bay, NE Baltic Sea

Macrozoobenthic communities within and outside of the drift algal mats were compared in Kõiguste Bay, NE Baltic Sea. The patches of the drift algae were on average 0.5–1 km wide in diameter covering about 25% of the total bottom area of the bay. Thickness of the mat did not exceed 6 cm. The biomass of the mat varied between 35 and 1391 g dw m^?2. The drift algal mats had no clear negative effect on macrozoobenthos except for a few infaunal species. The drift algae favoured several detrivorous, herbivorous and carnivorous species. Among the studied variables, the thickness of algal mat and oxygen concentration at near-bottom layer explained the best the structure of macrozoobenthos. Total number of invertebrate species increased curvilinearly with the thickness of algal mat having the peak value at 3–5 cm thick algal mat. To conclude, moderate drift algal mats increased habitat complexity and, thus, the diversity of benthic faunal assemblages in otherwise poorly vegetated coastal areas.     

General Description of Partly Meromictic Hypertrophic Lake Verevi,its Ecological Status,Changes during the Past Eight Decades,and Restoration Problems

The present study describes generally the ecosystem of Lake Verevi while more detailed approaches are presented in the same issue. The main task of the article is to estimate long-term changes and find the best method for the restoration of good ecological status. Lake Verevi (surface 12.6 ha, mean depth 3.6 m, maximum depth 11 m, drainage area 1.1 km², water exchange 0.63-times per year) is a hypertrophic hard-water lake located in town Elva (6400 inhabitants). Long-term complex limnological investigations have taken place since 1929. The lake has been contaminated by irregular discharge of urban wastewaters from oxidation ponds since 1978, flood from streets, and infiltrated waters from the surrounding farms. The so-called spring meromixis occurred due to extremely warm springs in recent years. The index value of buffer capacity of Lake Verevi calculated from natural conditions is on the medium level. Water properties were analysed according to the requirements of the EU Water Framework Directive. According to the classification, water quality as a long-term average of surface layers is moderate-good, but the water quality of bottom layers is bad. Values in deeper layers usually exceed 20–30 times the calculated reference values by Vighi and Chiaudani’s model. Naturally, at the beginning of the 20th century the limnological type of the lake was moderately eutrophic. During the 1980s and 1990s the ecosystem was out of balance by abiotic characteristics as well as by plankton indicators. Rapid fluctuations of species composition and abundance can be found in recent years. Seasonal variations are considerable and species composition differs remarkably also in the water column. The dominating macrophyte species vary from year to year. Since the annual amount of precipitation from the atmosphere onto the lake surface is several times higher, the impact of swimmers could be considered irrelevant. Some restoration methods were discussed. The first step, stopping external pollution, was completed by damming the inlet. Drainage (siphoning) of the hypolimnetic water is discussed. Secondary pollution occurs because Fe:P values are below the threshold. The authors propose to use phosphorus precipitation and hypolimnetic aeration instead of siphoning.     

安徽南漪湖大型底栖动物群落结构

2002年7月至2004年7月,对安徽南漪湖12个采样点的大型底栖动物群落结构进行了调查研究,共获得大型底栖动物39种,隶属于3门28属。大型底栖动物的现存量在2003年冬季出现最高值,密度最低值出现在2004年夏季。软体动物的现存量占绝对优势,其优势种为河蚬(Corbicula fluminea)、梨形环棱螺(Bellamya purificata)、铜锈环棱螺(B.aeruginosa)和长角涵螺(Alocinma longicornis)。Shannon-Wiener多样性指数、Margalef多样性指数和Pielou指数的年均值分别为0.83、0.51和0.77。南漪湖西部物种数、物种多样性、现存量均较东部高。建闸蓄水后,南漪湖的环境发生了很大的改变,随水深增加,大型底栖动物的现存量呈明显下降的趋势。     

Integrated lake monitoring in Europe the macrozoobenthos in the four target lakes in Finland

In four small ( 1 km²) Finnish lakes belonging to the Integrated Monitoring Programme (UN ECE), macrozoobenthos has been studied at different depths since 1989. The lakes are situated between 61°N–70°N latitudes from the southern boreal coniferous region up to the forest tundra ecotone. The macrozoobenthos of the lakes was very different compared to each other, but chironomids were important in all lakes. Acid-sensitive taxa (molluscs, some mayflies) were lacking in one of the lakes because of its low pH. In all lakes the zoobenthos could indicatee.g. the wideness of the littoral region and stagnation conditions or groundwater input through the bottom. In future, both litoral and profundal sampling is needed because of the multi-purpose character of the monitoring (acidification, trophic level).     

Long- and short-term Changes of the Macrophyte Vegetation in Strongly Stratified Hypertrophic Lake Verevi

The aim of study was to bring out changes in the macrophyte vegetation, caused by eutrophication, short-term lowering of the water level and the following restoration of equilibrium in L. Verevi. Also biomass and N and P content of shoots of main submergent species were studied in 1999–2001, to follow the temporal and specific differences. Due to strong eutrophication, the type of the lake changed from a Myriophyllum-Potamogeton-Charophyta lake to a Ceratophyllum-Lemna trisulca lake in 1984–1988, obviously owing to the formation of loose organic-rich sediment. Water lowering by 0.7 m during summer months of 1998 facilitated mineralization of sediments, as a consequence of which a mass development of Ranunculus circinatus and a temporary increase in the abundance and biomass of other nutrient-demanding species took place during following years. Our data suggest differences in nutrient supply and release of submerged species and the need for more species-related approach to this group. The problem of nutrient supply of unrooted plants at the time of stratification arises. Regarding the increase of biomass of Ceratophyllum demersum in second half of summer, we suppose that one part of nutrients for this growth may derive from freshly decayed filamentous algae or vascular plants.     

浙江分水江水库大型底栖动物群落结构及水质评价

2008年11月-2009年10月,在浙江桐庐分水江水库设置7个站点对大型底栖动物进行逐月调查.结果表明:调查共采集到37种底栖动物,主要由寡毛纲和摇蚊科物种组成.春、夏、秋季优势种均为霍甫水丝蚓,冬季优势种为羽摇蚊.直接收集者在物种数量、密度和生物量上均占绝对优势.群落年均密度和年均生物量分别为(488.0±48.8) ind·m-2和(1.86±0.49) g·m-2.底栖动物密度在站点间无明显差异但存在显著的季节变化,呈现春季＞夏季＞冬季＞秋季的趋势,生物量在站点、季节间均无显著差异.水温和水深是影响底栖动物时空分布的主要因子.Shannon多样性指数和Goodnight-Whitley指数不适合用于该水库的水质评价,其他指数综合显示分水江水库属于轻度污染.