Rates of ammonia release from sediments by chironomid larvae

SUMMARY. 1. Microcosms of Lake Balaton mud and sterilized sand and aerated water were used to evaluate ammonia increments in the overlying water as influenced by chironomid density and temperature. In the two approaches, the effects of sediment disturbance and metabolic excretion of chironomids were measured.
2. The activity of larvae increased the ammonia content of the overlying water at temperatures above 10°C. A rise of temperature to 20°C resulted in a 5–20-fold increase in ammonia release in both systems with chironomids.
3. At 10°C combined effects of sediment disturbance and of excretion produced lower release rates than did excretion rates alone (mud-water v. sand-water treatments). At higher temperatures (15 and 20°C) release rates of ammonia by sediment disturbance plus excretion were higher than excretion rates alone. Ammonia excretion contributed significantly to the total release at each temperature.
4. Metabolic mineralization of nitrogen compounds appears to be an important mechanism contributing to nitrogen regeneration from aerobic lake sediments. High N:P ratio (14:1) of chironomid excretion materials supports this interpretation.     

The impact of Chironomus plumosus larvae on organic matter decay and nutrient (N, P) exchange in a shallow eutrophic lake sediment following a phytoplankton sedimentation

The importance of Chironomus plumosus larvae onbenthic metabolism and nutrient exchange across thesediment–water interface was evaluated in a shalloweutrophic lake (Lake Arreskov, Denmark) following aphytoplankton sedimentation. Chironomus plumosuslarvae were added to laboratory sediment microcosms,corresponding to a density of 2825 larvae m⁻².Non-inhabited microcosms served as controls. Asedimentation pulse of organic matter was simulated byadding fresh algal material (Chlamydomonasreinhardii) to sediment cores (36 g dryweight m⁻²). The mineralization was followed bymeasuring fluxes of O₂, CO₂, dissolvedinorganic nitrogen and phosphate. A rapid clearance ofalgae from the water column in faunated microcosmssuggested that chironomids may be of major importancein controlling phytoplankton concentrations in shalloweutrophic lakes. Chironomids increased the sedimentO₂ uptake ≈ 3 times more than what wouldbe expected from their own respiration, indicating astimulation of microbial activity and decomposition oforganic matter in the sediment. Addition of algaeenhanced the release of CO₂, NH⁺ ₄ ando-P. The excess inorganic C, N and P released inamended non-inhabited sediment after 36 dayscorresponded to 65, 31 and 58% of the C, N and P inthe added algae. In sediment inhabited by Chironomus plumosus the corresponding numbers were147, 45 and 73%, indicating that mineralization oforganic matter also from the indigenous sediment poolwas stimulated by chironomids. This revised version was published online in July 2006 with corrections to the Cover Date.     

Phosphorus release from sediments in a river-valley reservoir in the northern Great Plains of North America

Aside from a companion investigation to this study, there are currently no peer-reviewed phosphorus (P) release rate data for northern North American (i.e., Canadian) reservoirs. Using Lake Diefenbaker, Saskatchewan, Canada as a case study, we tested the effect of variation in overlying water DO conditions on the P release rates from sediment cores. Sediment cores from four down-reservoir locations in Lake Diefenbaker were incubated under high (>8 mg l⁻¹), low (2–3 mg l⁻¹), or anoxic (<1 mg l⁻¹) DO concentrations. Sediment cores were then analyzed for total P (TP) and three geochemical P fractions to assess how the DO regime influenced sediment P inventory. Maximum P release rates were highest under anoxic conditions and similar among sites (15.0–20.3 mg m⁻² day⁻¹), with the low-DO rates intermediate to the high-DO and anoxic P fluxes. Predictive internal P loading models considering only hypolimnetic anoxia may therefore oversimplify and thus underestimate P mobilization in situ. Non-apatite inorganic P (54 ± 10% across sites) from the top 1 cm of the sediment profile was the main source of P released during incubations, indicating that sampling on a coarser scale of resolution could obscure the relationship between sediment geochemistry and short-term P flux.

     

The importance of sediment phosphorus release in the restoration of very shallow lakes (The Norfolk Broads,England) and implications for biomanipulation

Phosphorus release from the sediments of very shallow lakes, the Norfolk Broads, can be as high as 278 mgP m^-2 d^-1. These high rates are associated with high total sediment Fe:P ratios and occur when sulphide from sulphate reduction removes Fe(II) from the pore water. There is also evidence that bioturbation from benthic chironomids can enhance phosphorus release rates, particularly in sediments low in total iron. The release of phosphorus from the sediments of these lakes is delaying restoration following the control of phosphorus from sewage discharges. Biomanipulation is being used in these lakes to create clear water and re-establish aquatic macrophytes. This removal of fish has allowed larger populations of benthic chironomid larvae to develop which may result in an increase in the rate of phosphorus release and changes to the pore profiles of dissolved phosphorus, soluble iron and free sulphide.     

The Availability of Condensed Phosphates for the Algal Strain Scenedesmus obtusiusculus Chodat,with Special Regard to Conditions Characteristic in Lake Balaton

The limiting factor in the water of Lake Balaton was calculated by means of Verduin's equation. If only the orthophosphate-phosphorus concentration is inserted into the equation, phosphorus is the primary limiting factor. If, however, total phosphorus is considered, the factor intensity of nitrogen will be the least, i. e. nitrogen will be the primary limiting-factor of plant growth. According to measurements during 1976, average values for the total dissolved phosphorus and orthophosphate-phosphorus content of Balaton Lake water were 15,66 mg/m³ and 7.66 mg/m³, respectively. Experiments with the algal strain Scenedesmus obtusiusculus Chod. (Chlorophyceae, Chlorococcales). were designed to test the availability of the condensed phosphorus form for the algae. The experiments were performed partly with synthetic polyphosphates, partly, with polyphosphates isolated from Balaton Lake water. The results showed, contrary to our expectations, that phosphates present in the condensed form (irrespective of their structure and degree of condensation). were not utilized by the algae under sterile conditions, i. e. in the absence of bacterial activity. In the light of the above it is recommended to consider only orthophosphate-phosphorus when calculating the limiting factor.     

Studies on the biology of Chaoborus flavicans (Meigen) (Diptera: Chaoboridae) in a fish-free eutrophic pond,Japan

Population dynamics of Chaoborus flavicans larvae of various instars was studied from November 1986 to December 1987 in a eutrophic, fish-free pond, Japan. First and 2nd instar larvae were observed from late April to late October, indicating a reproductive period of about half a year. C. flavicans overwintered in the 4th instar larvae. In water column samples, total density of all instars was 680–23680 m^-2, and pupal density 0–2600 m^-2; larvae of the 1st, 2nd, and 3rd instars showed 5–6 density peaks in 1987, suggesting that 5–6 generations occur during a year (peaks of the 4th instar larvae were not clear, probably due to their longer development than those of younger instars). In sediment samples, no 1st and 2nd instar larvae were found, 3rd instar larvae were found occasionally but density of the 4th instar larvae was 280–18600 m^-2, and pupal density varied between 0–502 m^-2. Fouth instar larvae accumulated in sediment in the cold season and in the water column in the warm season; high temperature and low oxygen concentration were the most important factors limiting the distribution of larvae in the sediment in summer in the NIES pond. The dry weight of total C. flavicans larvae was 0.08–4.2 g m^-2 in sediment samples and 24–599 μg l^-1 (0.10–2.40 g m^-2) in water column samples. Comparisons of maximum densities in the NIES pond in different years and in waters of different trophic status show that density is generally higher in eutrophic than in oligotrophic habitats. This revised version was published online in July 2006 with corrections to the Cover Date.     

杭州西湖北里湖沉积物氮磷内源静态释放的季节变化及通量估算

通过采集北里湖不同季节的柱状芯样,在实验室静态模拟沉积物氨氮(NH+4-N)和可溶解性磷酸盐(PO3-4-P)的释放,同时研究了沉积物间隙水中NH+4-N及PO3-4-P的垂直分布特征.结果表明,沉积物间隙水NH+4-N随深度的增加有上升的趋势,PO3-4-P随深度的增加呈先升后降的趋势.氮、磷营养盐在沉积物—水界面均存在浓度梯度,表明存在自间隙水向上覆水扩散的趋势.沉积物NH+4-N在春季、夏季、秋季、冬季的释放速率分别为0.074 mg·m-2· d-1、0.340mg· m-2· d-1、0.087 mg· m-2· d-1、0.0004 mg·m-2·d-1,pO3-4-P的释放速率则分别为0.340 mg·m-2·d-1、0.518 mg·m-2·d-1、0.094 mg·m-2·d-1、-0.037 mg· m-2·d-1.不同采样点表现出明显的季节和空间差异性,释放速率表现为夏季＞春季、秋季＞冬季.根据静态模拟出的不同季节下内源氮、磷释放速率计算,全湖内源氮、磷营养盐的贡献分别为0.0037、0.0057t/a.该研究可为北里湖富营养化及内源污染的治理提供基础数据.     

Forms and Mobility of Sediment Phosphorus in Shallow Eutrophic Lake Võrtsjärv (Estonia)

The surficial sediment (0–10 cm) of shallow eutrophic Lake Võrtsjärv (Estonia) was characterized by an acid insoluble residue of 50% dry weight and low nutrient, Fe and Mn content. Among phosphorus (P) fractions (Hieltjes and Lijklema , 1980), NaOH-NRP amounted on an average to 50%, HCl-RP to 30%, NaOH-RP to 16%, and NH₄Cl-RP to 4% of their sum. Seasonal changes in sediment P content were inconsistent with mass balance calculations and could be attributed to sediment redistribution caused by decreasing water level. High Fe/P ratio (26–30) and the aeration of surficial sediment by frequent resuspension kept phosphate adsorbed. Low pore-water SRP (commonly <10 μg l⁻¹) usually prevented phosphate release from surficial sediment. However, a storm in September 1996 (max. wind speed 16 m s⁻¹) which coincided with the extremely low water level in the lake (mean depth 1.44 m), denuded deeper anoxic sediment layers and caused a SRP release of 193 mg P m⁻² d⁻¹.     

Effects of Phoslock® treatment and chironomids on the exchange of nutrients between sediment and water

Effects of chironomids on sediment–water exchange of nutrients and their impact on the efficiency of Phoslock^® (a lanthanum (La) modified clay for phosphorus (P) removal in freshwater systems) were tested during a 35 days incubation experiment with sediment cores from a Danish eutrophic Lake. Four different sediment treatments with increased or natural densities of chironomids in combination with Phoslock^® were used: (1) Control + (2) Chironomids + (3) Phoslock + (4) Chironomids & Phoslock. Nutrients in the overlying water were followed during the incubation period. The treatments with Phoslock reduced P in the overlying water significantly compared to the control treatment. In addition, the chironomids significantly increased sediment nitrate uptake as well as sediment ammonium release. After the incubation period, a sequential extraction of P and La was conducted. The Phoslock treatment led to a reduction of the iron-bound P pool in the sediment and a higher HCl-extractable P pool. Also, most La was recovered in the HCl extract, indicating that P became strongly bound to La in the Phoslock matrix. Sequential extraction of pure Phoslock demonstrated that the bentonite matrix of Phoslock contained redox sensitive iron, and that ammonium might be released from Phoslock, when dispersed in water.     

Substance and energy flows formed by the emergence of amphibiotic insects across the water–air boundary on the floodplain lakes of the Volga River

Substance flow across the water–air boundary on the floodplain Lake Holodnoe (Saratov oblast) is generally formed by the Culicomorpha (76.1%) and accounts for 0.35 g/m² of the lake area per year. The energy flow amounts to 1.87 kcal/m², and most of it accounts for the second half of summer and autumn. Annual removal of biogenic elements is 0.18 g/m² for carbon, 0.04 g/m² for nitrogen, and 0.004 g/m² for phosphorus. The greatest contribution to flows of substance and energy is brought by large species of chironomids, as well as chaoborids and medium-sized chironomids, which produce several generations within a year and reach high abundance at a larval stage. Other floodplain lakes of the Volga River with similar biotopical features and species composition of amphibiotic insects are characterized by a quantitatively similar level of exchange processes with adjacent land ecosystems across the water–air boundary.     

The influence of chironomus plumosus larvae on the exchange of dissolved substances between sediment and water

4th instar Chironomus plumosus larvae (about 1000·m^–2) were added to tubes containing sediment and overlying water. At a temperature of 20°C the larvae greatly increased the trasnport of silica, phosphorus and iron from the sediment to the water. Oxygen concentrations did not influence the exchange of silica. For two non-calcareous sediments the exchange of phosphorus and iron was much higher under anaerobic than under aerobic conditions while the difference was small for sediment from a hardwater lake. Exchange of inorganic nitrogen was little influenced by added chironomid larvae.     

Interactions between sediment and water in a shallow and hypertrophic lake: a study on phytoplankton collapses in Lake Søbygård,Denmark

Short-term changes in phytoplankton and zooplankton biomass have occurred 1–3 times every summer for the past 5 years in the shallow and hypertrophic Lake Søbygård, Denmark. These changes markedly affected lake water characteristics as well as the sediment/water interaction. Thus during a collapse of the phytoplankton biomass in 1985, lasting for about 2 weeks, the lake water became almost anoxic, followed by rapid increase in nitrogen and phosphorus at rates of 100–400 mg N M^–2 day^–1 and 100–200 mg P m^–1 day^–1. Average external loading during this period was about 350 mg N m^–2 day^–1 and 5 mg P m^–2 day^–1, respectively.Due to high phytoplankton biomass and subsequently a high sedimentation and recycling of nutrients, gross release rates of phosphorus and nitrogen were several times higher than net release rates. The net summer sediment release of phosphorus was usually about 40 mg P m^–2 day^–1, corresponding to a 2–3 fold increase in the net phosphorus release during the collapse. The nitrogen and phosphorus increase during the collapse is considered to be due primarily to a decreased sedimentation because of low algal biomass. The nutrient interactions between sediment and lake water during phytoplankton collapse, therefore, were changed from being dominated by both a large input and a large sedimentation of nutrients to a dominance of only a large input. Nitrogen was derived from both the inlet and sediment, whereas phosphorus was preferentially derived from the sediment. Different temperature levels may be a main reason for the different release rates from year to year.     

Temporal distribution of larval Chironomidae (Diptera) in experimental rice fields in Penang,Malaysia

The distribution and abundance of chironomid larvae were investigated in experimental rice fields at the Bukit Merah Agricultural Experimental Research Station, Penang, Northern Malaysia. The mean density of chironomid larvae during the period of the study (including two cultivation seasons) was 121 larvae m^?2. Chironomus kiiensis (48.6%) was the most abundant species, while four other species, Polypedilum trigonus (4.8%), Tanytarsus formosanus (22.6%), Tanypus punctipennis (13.9%), and Clinotanypus sp. (10.1%) occurred less frequently, although they were present during all wet phases of rice cultivation. Generally, water depth, rice plant height, conductivity, and nitrate–nitrogen content of the water only weakly influenced the abundance of the larvae. Other environmental parameters such as pH, dissolved oxygen, daytime water temperature, total suspended solids, phosphate, and sediment total organic matter did not significantly affect larval populations. The community structure of chironomids in this rice agroecosystem followed the dynamic changes of the field including agronomic practices, patterns of water availability, and phases of rice plant growth.     

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.     

Measurement and verification of rates of sediment phosphorus release for a hypereutrophic urban lake

The contribution of sediment release to the phosphorus budget of hypereutrophic Onondaga Lake was determined through laboratory measurements made on intact cores. Rates ranged from 9–21 mg P m^–2 d^–1 with a mean of 13 mg P m^–2 d^–1, values similar to those observed in other lakes of comparable trophic state. There was no statistically significant trend in rates in time (July versus September) or in space (location along the major N/S axis of the lake). Rates of sediment phosphorus release measured in the laboratory compared favorably with the observed rate of soluble reactive phosphorus accumulation in the lake's hypolimnion. The sediments are the second largest source of phosphorus for Onondaga Lake, contributing 24% of the overall phosphorus load to the system.     

Eight years of internal phosphorus loading and changes in the sediment phosphorus profile of Lake Søbygaard,Denmark

During each of the first 8 years following an 80–90% reduction in external phosphorus loading of shallow, hypertrophic Lake Søbygaard, Denmark in 1982, phosphorus retention was found to be negative. Phosphorus release mainly occurred from April to October, net retention being close to zero during winter. Net internal phosphorus loading was 8 g P m^–2 y^–1 in 1983 and slowly decreased to 2 g P m^–2 y^–1 in 1990, mainly because of decreasing sediment phosphorus release during late summer and autumn. The high net release of phosphorus from Lake Søbygaard sediment is attributable to a very high phosphorus concentration and to a high transport rate in the sediment caused by bioturbation and gas ebullition. Sediment phosphorus concentration mainly decreased at a depth of 5 to 20 cm, involving sediment layers down to 23 cm. Maximum sediment phosphorus concentration, which was 11.3 mg P g^–1 dw at a depth of 14–16 cm in 1985, decreased to 8.6 mg P g^–1 dw at a depth of 16–18 cm in 1991. Phosphorus fractionation revealed that phosphorus release was accompanied by a decrease in NH₄Cl-P + NaOH-P and organic phosphorus fractions. HCl-P increased at all sediment depths. The Fe:P ratio in the superficial layer stabilized at approximately 10. Net phosphorus release can be expected to continue for another decade at the present release rate, before an Fe:P ratio of 10 will be reached in the sediment layers from which phosphorus is now being released.     

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.     

Effect of light intensity and eye development on prey capture by larval striped bass Morone saxatilis

The efficacy of visual and non-visual feeding among pelagic striped bass Morone saxatilis larvae adapted to a turbid estuary was determined in the laboratory in clear water. Capture of Artemia salina (density 100 l⁻¹) was significantly affected by the interaction between age of larvae (range: 8–25 days post-hatch, dph) and light intensity (range: 0–10·6 μmol s⁻¹ m⁻² at the water surface). Visual feeding by larvae aged 9–11 dph was highest in dim light (0·086–0·79 μmol s⁻¹ m⁻²), with fish capturing up to 5 prey larva⁻¹ h⁻¹. As the larvae grew, prey capture in brighter light improved, associated with an increasing proportion of twin cone photoreceptors and improving ability of the retina to light- and dark-adapt. By age >22 dph, mean prey capture was greatest at highest light intensities (0·79 and 10·6 μmol s⁻¹ m⁻²) exceeding 100 prey larva⁻¹ h⁻¹. Incidence of feeding larvae generally improved as the larvae grew, reaching >80% in all light intensities from 16 dph onwards. The lower threshold for visual feeding, between 0·0084 and 0·03 μmol s⁻¹ m⁻², remained constant as the larvae grew, despite an increasing density of rod photoreceptors. Below this threshold, non-visual feeding was evident at a low rate (<6 prey larva⁻¹ h⁻¹) that was independent of larval age.     

杭州西湖北里湖荷叶枯落物分解及其对水环境的影响

湖泊水生植物枯落物的分解过程影响着枯落物的淤积以及营养元素向水体和底泥的释放,进而影响湖泊水环境。用分解袋法研究了杭州西湖北里湖荷叶枯落物的分解速率和营养动态。荷叶枯落物的分解速率表现快慢交替的阶段性特点,分解速率常数峰值出现在6月,其余时段呈现波动状态。枯落物氮、磷含量变化趋势基本一致,呈现下降-逐渐上升-渐趋稳定的变化特点。氮、磷积累指数(NAI)呈现释放-积累-释放,整体以释放为主的变化特征。在此基础上推算了北里湖荷叶枯落物一个分解周期残留量的变化及氮、磷释放情况,探讨枯落物分解对水环境的影响。荷叶枯落物入湖量以立枯体总量的20%估算,残留量从11月至翌年1月急剧增加,在1月底达到峰值,随后持续下降,至10月底尚残留1.675 t干重,合30.45 kg/m²干重(按荷塘面积计算),与残留量峰值相比减少了74.39%。枯落物分解导致的氮、磷释放在11月至翌年1月持续增高,2、3月份释放量趋于下降,4、5月份出现净积累,6-10月保持净释放。整个分解周期氮、磷总释放分别为92.247 kg和6.421 kg,相当于北里湖水中氮、磷含量分别增加0.143 mg/L和0.010 mg/L。由于挺水植物生长过程吸收的主要是沉积物中的氮、磷营养盐,因此,荷花的生长和枯落分解过程具有促进氮、磷从沉积物迁移到水体,增加水中氮、磷含量的作用。     

The effect of tubificids and chironomids on particle redistribution of lake sediment

The effects of chironomid larvae,Chironomus plumosus, and tubificid worms,Limnodrilus spp., on particle redistribution in lake sediment were investigated experimentally using pots containing sediments obtained from Lake Suwa, Japan. The chironomids and tubificids increased the water content of surface sediment. The chironomid larvae had no effect on particle size distribution, while tubificids continuously accumulated small particles on the surface sediment through their selective feeding activity. Particles larger than 0.125 mm were buried at a sediment depth of 6 cm. In Lake Suwa, long diatom frustules, large plant debris and blue-green algal flocs were found to accumulate in the deeper layer of the lake sediment inhabited by tubificids at high density.