Retention time as a primary determinant of colour and light attenuation in two tropical Australian reservoirs

1. The light climates of Darwin River Reservoir (DRR) and Manton River Reservoir (MRR), in northern Australia, are compared for an 8-year period. The reservoirs are subject to the same wet/dry tropical climate and have similar catchment characteristics, but differ in their basin morphology, retention time and trophic status.
2. Median euphotic depths in DRR and MRR were 9.7 and 4.4 m, respectively. Seasonal variation in each reservoir's euphotic depth was best explained by colour, based on a stepwise linear regression. Turbidity was excluded from the two regressions, while chlorophyll a concentration was significant only for the MRR regression.
3. Both reservoirs showed the same seasonal pattern for colour. Wet season inflow increased reservoir colour, and was followed by a reduction in colour due to photodegradation and microbial decomposition of humic material, reaching a minimum before the next wet seasons inflow.
4. Although the colour of catchment run-off into both reservoirs was similar, MRR colour was two to three times greater than that measured in DRR. The higher colour and greater light attenuation of MRR is attributed primarily to its shorter retention time, and therefore shorter time for colour removal. Annual retention time accounted for 97% of the variability of average annual colour (measured as absorption at 440 nm), based on a linear regression of log₁₀ transformed data for both reservoirs.
5. Long retention times favour reduced colour, increasing water transparency, particularly in water bodies of low trophic state and inorganic turbidity.     

Retention time as a primary determinant of colour and light attenuation in two tropical Australian reservoirs

1. The light climates of Darwin River Reservoir (DRR) and Manton River Reservoir (MRR), in northern Australia, are compared for an 8-year period. The reservoirs are subject to the same wet/dry tropical climate and have similar catchment characteristics, but differ in their basin morphology, retention time and trophic status.
2. Median euphotic depths in DRR and MRR were 9.7 and 4.4 m, respectively. Seasonal variation in each reservoir's euphotic depth was best explained by colour, based on a stepwise linear regression. Turbidity was excluded from the two regressions, while chlorophyll a concentration was significant only for the MRR regression.
3. Both reservoirs showed the same seasonal pattern for colour. Wet season inflow increased reservoir colour, and was followed by a reduction in colour due to photodegradation and microbial decomposition of humic material, reaching a minimum before the next wet seasons inflow.
4. Although the colour of catchment run-off into both reservoirs was similar, MRR colour was two to three times greater than that measured in DRR. The higher colour and greater light attenuation of MRR is attributed primarily to its shorter retention time, and therefore shorter time for colour removal. Annual retention time accounted for 97% of the variability of average annual colour (measured as absorption at 440 nm), based on a linear regression of log₁₀ transformed data for both reservoirs.
5. Long retention times favour reduced colour, increasing water transparency, particularly in water bodies of low trophic state and inorganic turbidity.     

三座南亚热带大型水库敞水区桡足类群落结构比较

于2000-2002年对南亚热带三座大型水库:新丰江水库、公平水库和飞来峡水库敞水区桡足类进行了定性定量采样.三座水库桡足类种类数较少,共检出桡足类4科10属14种,其中8种哲水蚤,5种剑水蚤和1种猛水蚤.主要分布在广东省水库的我国特有种舌状叶镖水蚤(Phyllodiaptomus tunguidus)和广布性种类右突新镖水蚤(Neodiaptomus schmackeri)是出现频率较高的哲水蚤种类,温中剑水蚤(Mesocyclops thermocyclopoides)、台湾温剑水蚤(Thermocyclops taihokuensis)和博平近剑水蚤(Tropocycl opsbopingi)是出现频率较高的剑水蚤种类.水库的流域面积、滞留时间、鱼类捕食和营养状态是影响水库桡足类种类组成和数量的重要因素.三座水库桡足类种类数与水库流域面积大小存在正相关关系.随着水库营养水平的升高,桡足类密度和生物量也相应增加,但是大型哲水蚤的优势度降低,而剑水蚤和桡足类幼体的优势度上升.水力滞留时间很短是引起飞来峡水库桡足类种群波动的主要因素.水库捕食性鱼类对甲壳浮游动物的选择性捕食,对桡足类种类影响较小,对桡足类成体密度影响较大.由于地区差异和鱼类捕食强度等因素的影响,桡足类种类多样性与水体营养状态之间存在不确定性.     

Assessing ecological water quality of freshwaters: PhyCoI—a new phytoplankton community Index

We propose and test a new Phytoplankton Community Index (PhyCoI) for monitoring the ecological status of lakes and reservoirs. The design of our PhyCoI is based on the fact that phytoplankton biomass and community structure respond to changes in water quality (mainly eutrophication) and by themselves also influence water quality. In order to accommodate this double role of phytoplankton as indicator and impact, PhyCoI is based on phytoplankton community properties at different hierarchical levels combining both specific metrics (total biomass, taxonomic group biomass, cyanobacteria contribution, taxonomic group species richness) and new or modified sub-indices. It is calculated from the scores of the different metrics/sub-indices resulting in a final index value in the range from 0 to 5, to assess water quality on the basis of five ecological classes according to the Water Framework Directive (WFD). The test of PhyCoI was based on Carlson's Trophic State Index (TSI_SD) based on water transparency (Secchi depth) in 26 Greek lakes and reservoirs covering the entire spectrum from oligotrophic to hypertrophic. A highly significant relationship at p < 0.001 between the two variables was found, with the values of the PhyCoI declining with increasing TSI_SD. Furthermore, a significant relationship between the PhyCoI and land use types at the watershed of the studied freshwaters was found identifying permanent crops, pastures and shrubs and herbaceous vegetation associations as significant predictors of PhyCoI values. Because of the amount of labor involved in obtaining the PhyCoI we suggest to combine low frequency PhyCoI determinations with a high frequency Secchi depth measurements for practical monitoring purposes.     

Catchment land use and trophic state impacts on phytoplankton composition: a case study from the Rotorua lakes’ district, New Zealand

Trophic state of lakes has been related to catchment land use, but direct links between phytoplankton taxa and land use are limited. Phytoplankton composition, represented by relative cell abundance of phyla, was measured over a period of 4 years in 11 lakes in the Rotorua region, New Zealand. The lakes differed in morphometry, trophic state and land use (as percentage catchment area). We tested whether relative proportion of land uses, indirectly representing relative nutrient loading, was the overarching driver of phytoplankton composition. Trophic state was correlated negatively with native forest and positively with pasture and urban area. Cyanoprokaryota were correlated negatively with native forest and positively with pasture and trophic state, Chlorophyta were correlated positively with native forest and urban land use and negatively with pasture and trophic state, and Bacillariophyta were positively correlated with dissolved reactive silica to dissolved inorganic nitrogen (Si:DIN) and Si to dissolved reactive phosphorus (Si:DRP) ratios. Lakes with higher nutrient loads had higher trophic state and Cyanoprokaryota dominance. Chlorophyta were negatively correlated with Cyanoprokaryota and Bacillariophyta, suggesting competition amongst these groups. Our results apply to lakes potentially subject to changes in catchment land use, which may have implications for trophic state, phytoplankton composition and Cyanoprokaryota blooms.     

Trophic state of a lowland reservoir during 10 years after restoration

The restored Maltañski Reservoir was studied from its filling with water in 1990 till 2000. Total phosphorus, chlorophyll-a, and Secchi depth, as well as the Carlson's trophic state index (TSI) values based on those three parameters showed characteristic patterns of changes among seasons and years. Within each year, the lowest trophic state was usually observed in winter and the highest in summer. Because of the high loads of phosphorus received by the reservoir, this element did not limit primary production. TSI values calculated on the basis of total phosphorus were always markedly higher than calculated on chlorophyll-a and Secchi depth (similar to each other). The trophic upsurge phase lasted only a few months after the filling of the reservoir in 1990. Similar symptoms were observed after its refilling in the spring of 1993. The trophic depression phase lasted until the end of 1995. After that time a significant correlation between phosphorus concentration in the reservoir and in river waters flowing into the reservoir was observed. The successive phases of reservoir ageing, determined on the basis of phosphorus concentration, were not accompanied by changes in chlorophyll-a content. The influence of the top-down mechanism (biomanipulation effect) resulted in relatively low values of chlorophyll-a after the filling of the reservoir with water in 1990 and in 1993. As early as 1992 chlorophyll-a values reached a very high level and stayed at that level until the end of the study in 2000 (except for the short decline in 1993).

     

The Trophic Index of Macrophytes (TIM) – a New Tool for Indicating the Trophic State of Running Waters

In running waters, apart from structural degradation, nutrient input becomes increasingly important. To investigate the indicator values of as many species of submerged macrophytes as possible numerous samples of the sediment within macrophyte stands and the overlying water were taken in running waters throughout Bavaria, Germany. To develop the Trophic Index of Macrophytes (TIM), the concentrations of soluble reactive phosphorus of both the water body and the sediment pore water were used. Based on a weighted sum of the SRP‐concentrations of the water body and the sediment pore water, indicator values were determined for a total of 49 species of submerged macrophytes. A detailed method is described on how and depending on which preconditions the trophic state of running waters can be determined by the TIM. An example of the TIM in the stream Rotbach is given. It shows that the TIM is a useful means to detect differences in the phosphorus loading of running waters.     

江西省余江县水体营养状况分析

用营养状态指数法(TSI)对江西省红壤区余江县东塘、五湖、仙塘三个水库的水质状况进行综合评价,结果表明三个水体的水质状况均呈富营养态。在此基础上对三个水库的10项主要水化学指标进行主成分分析,表明亚硝态氮和氨氮对第一主成分的贡献最大,COD为第二主成分的主要贡献者;而且三个水库的水质受水中有机物含量的影响最大,这一结果与当地的农业结构密切相关。     

Biomanipulation as a useful water quality management tool in deep stratifying reservoirs

In six deep, soft-water reservoirs, ranging from oligotrophic to eutrophic, fishery management has been guided by the use of biomanipulation to improve water quality and opportunities for recreational fishing. As evidenced by the establishment of larger-bodied daphnids, a low level of zooplanktivory could be maintained in the newly filled Grosse Dhünn and refilled Brucher and Lingese Reservoirs only by regular stocking of piscivores (Sander lucioperca, Esox lucius, Salmo trutta lacustris, Onchorhynchus mykiss) in combination with size and bag limitations for the recreational fisheries. However, in the mesotrophic Pre-Reservoir Grosse Dhünn, Bever Reservoir and the newly filled slightly eutrophic Wupper Reservoir it took between 8 and 10 years before the predator-resistant zooplankton community responded to management with a switch to larger daphnids. Except for oligotrophic Grosse Dhünn Reservoir where angling is prohibited, the expected enhancement of piscivore biomass through stocking not least was prevented by anglers. However, growth of perch (Perca fluviatilis) benefited from the changed fishery management relying upon stocking piscivores only allowing them to reach the size of piscivory. The appearance of larger daphnids in Pre-Reservoir Grosse Dhünn and Wupper Reservoir resulted in the biomass of the Daphnia spring peak to increase and occur earlier causing prolonged clear water conditions. Although the larger daphnids increased transparency, total summer mean chlorophyll concentrations in the euphotic zone only decreased in the slightly eutrophic reservoirs due to reduced phosphorus availability following unchanged external phosphorus loadings. Reduced phosphorus availability in these reservoirs caused a real oligotrophication. Although the edible seston fraction was controlled “top down” the results did not support the trophic cascade hypotheses because total phytoplankton remained controlled “bottom up”, admittedly triggered by “top down” forces. In general, the results support the importance of indirect (non-lethal) effects as the driving forces for the successful biomanipulations, particularly in slightly eutrophic reservoirs. Not least, the delayed zooplankton response provides an indication that the underlying change of internal feedbacks was not driven by external forces to stabilize the reservoirs trophic state in these deep stratifying reservoirs. Handling editor: D. Ryder     

罗非鱼对水质的影响

鱼类是影响水库等水质的重要因素,以我国南方主要养殖鱼类之一的罗非鱼为对象,通过广东大镜山水库原位围隔实验,研究了鱼类对水质的影响。结果表明,与对照组相比罗非鱼围隔中总氮,总磷和叶绿素a浓度分别升高了42%,129%和347%。罗非鱼的排泄增加了水体营养负荷,为浮游植物生长提供大量的营养盐,引起浮游植物生物量增加,水体透明度降低。罗非鱼通过营养盐释放所产生的上行效应明显大于由其牧食导致的下行效应。     

贵州山区新建水库浮游植物群落结构特征

对贵州山区新建水库的浮游植物群落结构特征进行研究,有利于了解同类水库的浮游植物群落演替趋势,还可以评估水华发生的潜在风险,为管理部门提供参考。贵州省六盘水市的观音岩水库和万营水库,分别为2018年和2017年建成蓄水的新建水库,文章以实地调查为基础对两座水库的浮游植物群落结构特征及其与环境因子关系进行了研究。2018年11月至2019年10月间的季度调查显示,两座水库分别检出32种和28种浮游植物,优势种均以硅藻和绿藻为主,藻类平均密度分别为3.46×10⁶和4.79×10⁶ cells/L。RDA分析结果显示,观音岩水库和万营水库浮游植物群落的主要驱动因子相同,均为水温(WT)、总磷(TP)和水体透明度(SD)。总体来说,新建水库在运行初期出现藻类暴发的风险较低,在后续管理中,应着重关注浮游植物密度受温度、外源营养及季节变化的影响。     

Trophic assessment of streams in Uruguay: A Trophic State Index for Benthic Invertebrates (TSI-BI)

Human activities are radically changing natural land cover and increasing the delivery of soil, organic compounds, nutrients, toxic agrochemicals and other contaminants to aquatic ecosystems. The eutrophication of streams, rivers, lakes, reservoirs and costal zones is one of the most important consequences of human activities. In this study we assessed the trophic status of 28 wadeable stream reaches of the Santa Lucía basin, an important economic region of Uruguay. We developed a Trophic State Index of Benthic Invertebrates (TSI-BI), the first of its kind for South American lotic systems. The methodological approach consisted of determining the ambient trophic gradient via canonical correspondence analysis based on the benthic invertebrate abundance matrix and an environmental variable matrix. The rescaled site scores served as environmental variables in the weighted averaging model (WA), to weight the benthic abundances and then find the optimum and tolerance of each of the sampled genus. These data were used to estimate the TSI-BI scores. These scores, in conjunction with the total phosphorus concentrations (TP), were used to group the study reaches when running a cluster analysis. The basic statistical parameters of the defined groups serve as an input to identify the threshold values of TP and TSI-BI corresponding with the different trophic states. The boundaries of TSI-BI and TP demarcating mesotrophic and eutrophic states were 8 and 71 μg/l, respectively, and can be considered the limits between impaired and less altered reaches. The results also indicated that the trophic status of the reaches is related to land use intensity. A change in land use management seems to be critical for the preservation of one of the most important water supply systems in Uruguay.     

Chlorophyll content and factors affecting its spatial distribution in the Middle Volga reservoirs

On the basis of the data obtained during field observations in the summer low water period of 2001, the patterns of chlorophyll distribution and its relation to hydrological and hydrochemical factors in two eutrophic reservoirs of the Middle Volga are studied. The hydrological structure of the Gorky Reservoir, where the Volga water mass dominates, is homogeneous, while in the Cheboksary Reservoir along with the eutrophic Volga waters, the mesotrophic Oka water masses can be distinguished keeping their abiotic and biotic features over a long distance. Phytoplankton in the two contiguous reservoirs with different flow regimens and anthropogenic loads responds differently to the external influence. An autotrophic community in the Gorky Reservoir is more stable and depends little on abiotic factors which account for ∼63% of the explained chlorophyll variation. In the Cheboksary Reservoir under maximal for the Volga cascade flow velocity and anthropogenic load, the development and distribution of phytoplankton are almost completely (R ² = 0.93) controlled by these factors. The trophic state of the reservoirs has not changed as compared to the beginning of the 1990s.     

广东省大中型供水水库营养现状及浮游生物的响应

于2000年调查了广东省18座大中型供水水库的水质现状并探讨了浮游生物对营养水平的响应。总氮、总磷、透明度和叶绿素a分别为0．15～7.15mg／L、0．003～0．387mg／L、0．4～6．3m和0．6～32．3ug／L。总氮、总磷、透明度均与叶绿素a呈较高的相关性。根据这4个因子的综合加权营养状态指数为23．7～55．1,季节差异不大,大多数水库处于中营养状态。金藻在中-富及富营养型水库中没有分布,而蓝藻、绿藻、硅藻和甲藻在调查水库中均有比较广的营养生态位,但它们的密度及相对优势度在各营养型水库中有一定的差异。高营养水平水库有较高的细胞密度和叶绿素a含量。营养水平较低的水库浮游植物以硅藻-甲藻、硅藻-绿藻或金藻-硅藻为主;营养水平较高的水库以蓝藻-硅藻或蓝藻-绿藻为主,并有较高的裸藻密度。浮游动物基本上以桡足类为优势种群,但在中-富营养和富营养型水库中,哲水蚤种类比低营养型水库中少。枝角类优势种类在各营养型水库差别不大。轮虫对水体营养水平的响应相对比较显著。低营养水平水库的轮虫以广营养型、中营养型或寡中营养型种类为主,种类数目比较少;富营养和中-富营养型水库的轮虫以喜在中营养到富营养条件下生长的种类为主,且轮虫种类数目比较多。     

Does reservoir trophic status influence the feeding and growth of the sharptooth catfish,Clarias gariepinus (Teleostei: Clariidae)?

The diet and growth of sharptooth catfish, Clarias gariepinus, in an oligotrophic system (Kat River Reservoir, Eastern Cape, South Africa) were compared to those in a eutrophic system (Laing Reservoir, Eastern Cape) to determine if the trophic status of a waterbody had an effect on the growth rate of the species. In order of importance, the diet of catfish in Kat River Reservoir consisted of fish, insects, zooplankton, plant material and other items, while the diet of catfish in Laing Reservoir consisted of fish, plant material, zooplankton, other vertebrates and insects. The diets of catfish in the two reservoirs had a similarity index of 68.1% and there was no significant difference in their nutritional value. Fish prey was the most important dietary component in both reservoirs. Temperature regime and zooplankton and zoobenthos density were similar in both systems. However, fish prey density was significantly higher in the eutrophic Laing Reservoir and catfish grew significantly faster in that system. The slower growth rate in Kat River Reservoir was attributed to the higher energy costs associated with the capture of fish prey, which was less abundant than in Laing Reservoir. Trophic status therefore had an indirect effect on catfish growth by influencing the availability of fish prey.     

Sources,concentrations and characteristics of organic matter in softwater lakes and streams of the Swedish forest region

18 Swedish forest lakes covering a wide range of dystrophy were studied in order to quantify and characterize the organic matter in the water with respect to origin (allochthonous or autochthonous), physical state (particulate or dissolved) and phosphorus content. Samples were collected repeatedly during a two-year period with unusually variable hydrological conditions. Water from three different depths and from tributaries was analysed with standard monitoring methods, including water colour, Secchi disk transparency, total organic carbon (TOC), COD_Cr, COD_Mn, total phosphorus and molybdate reactive phosphorus. Interrelationships were used to compare different methods and to assess the concentration and composition of organic matter. It is estimated that in remote softwater lakes of the Swedish forest region, autochthonous carbon is typically < 5 g m⁻³. Most lakes in this region receive significant amounts of humic matter originating from coniferous forest soils or peatland in the catchment area. In most humic lakes with a water colour of ≥ 50 g Pt m⁻³, more than half of the organic carbon in the surface water is of allochthonous origin, and in polyhumic lakes (> 200 g Pt m⁻³) the proportion can exceed 90%. Secchi depth readings were related similarly to organic matter from both sources and provided good estimates of TOC with a single optical measurement. Water colour was used to distinguish allochthonous and autochthonous matter. High concentrations of phosphorus were found in humic waters, most of it being molybdate reactive, and probably associated with humic matter rather than as dissolved free inorganic forms. COD_Mn yielded only 25–60% of TOC and appears to include mainly truly dissolved substances of low molecular weight.     

Trophic Classification of Non‐Perennial Reservoirs Utilized for the Development of Culture‐Based Fisheries,Sri Lanka

The aim of this study was to check the suitability of some trophic models developed for temperate regions to classify the non‐perennial reservoirs of Sri Lanka in order to manage culture‐based fisheries of those reservoirs. A limnological study was carried out in 45 non‐perennial reservoirs, which have been randomly selected for stocking of fish fingerlings for the development of culture‐based fisheries. High total phosphorous (TP) content in relation to algal biomass indicates high non‐algal turbidity in all reservoirs. Carlson's trophic state indices (TSI) measured on the basis of Secchi disc depth [TSI (SDD)], TP [TSI (TP)] and chlorophyll a [TSI (Chl‐a)] show that the 45 reservoirs studied are characterized by TSI (TP) = TSI (SDD) > TSI (Chl‐a), indicating that non‐algal particulate matter or colour dominates underwater light attenuation. As TSI (Chl‐a) is positively correlated to culture‐based fisheries yield, it is useful for planning culture‐based fisheries development strategies in non‐perennial reservoirs of Sri Lanka, and has the potential to be used elsewhere in the tropics for comparable developments. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ecological indicators based on trophic spectrum as a tool to assess ecosystems fishing impacts

Trophic indicators were used to compare two Malian freshwater reservoirs whose main differences are based on their different fishing pressures. Data were collected from a scientific survey of small-scale fishery landings conducted in 2002/2003. The trophic levels of fish species caught by artisanal fisheries are estimated from observations of scientific fishing or from the metabase Fishbase. Important differences exist in the trophic structure of both reservoirs. In Selingue (with high fishing pressure), very few top predators are found in the catches while the low trophic level fishes increase in total catches. In Manantali (with low fishing pressure), the top predators contribute twice as much to catches compared to Selingue. Hence, the mean trophic level of catches in Selingue (2.80) is lower than in Manantali (2.97). When comparing these results with those of study made in 1994/1995, it clearly appears that the effects of the fishing pressure in Selingue are obvious through a decrease of 0.12 in the mean trophic level while in Manantali this mean level has increased by 0.33 due to a recent strategic targeting of top predators. Trophic spectra seem to be relevant tools to characterize exploited fish communities from multi-specific and multi-gear small-scale fisheries catch data.     

广东大中型供水水库的磷污染与富营养化分析

2000年丰水期和枯水期对广东大中型水库的磷污染和富营养化现状进行了调查。结果表明,在调查的20个大中型供水水库中,一半以上的水库受到磷污染,磷污染已成为水库富营养化的重要原因。水库的总磷浓度与水库的营养状态基本一致。水库普遍存在磷限制现象,且枯水期的磷限制现象更为严重。在低温和磷限制条件下,硅藻比绿藻更加有优势。     

Cyanophytes and chlorophytes versus raphidophytes in humic lakes with different catchment basins

The aim of the study was to evaluate the effects of coniferous forest cover in the catchment basin and relative catchment area (catchment area to lake volume ratio) on phytoplankton composition in humic lakes. The study was carried out in 11 small and shallow lakes situated in the West Polesie region (Eastern Poland). The lakes were divided with respect to forest cover in their catchment basins into two groups: high forest cover — HFC (more than 60%) and low forest cover — LFC (less than 60%). The study showed that both, land use in the catchments (proportion of forests) and the relative catchment area determined physicochemical and biological parameters in the lakes. The high relative catchment area affects their high productivity expressed by high chlorophyll a concentration and low water visibility. The lakes of the LFC group had low water colour as well as high concentration of total phosphorus (P_tot), reaction (pH), and conductivity of water and a large number of cyanophytes and chlorophytes. The dominant species, e.g., Planktolyngbya limnetica, Limnothrix planctonica, Planktothrix agardhii, Coenococcus planctonicus, were characteristic of high trophic status. In the lakes of the HFC group, P_tot, pH, conductivity of water and the contribution of cyanophytes and chlorophytes was considerably lower, whereas the water colour and the number of raphidophytes represented by Gonyostomum semen was high. The large number of raphidophytes and the small amount of chlorophytes and cyanophytes in the lakes of the HFC group indicated the lake naturalness.