Freshwater biogeography in Wallacea: The case of sphaeriid bivalves in the Malili lake system (Sulawesi,Indonesia)

Ancient lakes are renowned as freshwater hotspots of biodiversity and endemism. However, some of these water bodies are poorly studied with the minute pill clams in the genus Pisidium (family Sphaeriidae) being particularly overlooked. The Malili lake system is located on Sulawesi, which is the largest and possibly biologically most diverse Indonesian island within the biodiversity hotspot region of Wallacea. This lake system consists of 5 interconnected lakes that harbour a unique freshwater fauna including 42 mostly endemic mollusc species described to date. The only bivalves recognized in this lake system have been in the widespread genus Corbicula. We present new insights into the sphaeriid biodiversity of the ancient Malili lakes and provide the first fossil-calibrated phylogeny for this family to discuss the biogeographical history of the Wallacean Pisidium fauna including the dating of speciation events. Both morphological and molecular data suggest that the Malili lake system is inhabited by at least three Pisidium species, two of which are potentially endemic to these lakes. This diversity is probably derived from a single colonization event from the Oriental region. The fossil-calibrated phylogeny further indicates that intra-island diversification occurred well after the island was fully formed. Our study improves understanding of the overall sphaeriid biodiversity in Indonesia as well as the endemic fauna of the ancient lakes.     

Seasonal variation in trophic structure and restoration effects in a deep perialpine lake (Lake Lugano,Switzerland and Italy)

Using monitoring data from the South Basin of Lake Lugano (Switzerland and Italy), we examined seasonal responses of phytoplankton and herbivorous zooplankton biomass to nearly three decades (1989–2017) of phosphorus (P) management to ask: [1] what is the trophic structure of the lake, [2] whether trophic structure and the effects of nutrient management varied seasonally, and [3] what are the implications of the existent trophic structure for the restoration of the lake. Trophic structure varied seasonally, including a structure consistent with strong consumer control (exploitation food chain) in spring and fall, and an unexpected structure in summer, characterized by a negative correlation between phytoplankton biomass and phosphorus. This structure was explained by accumulation of inedible phytoplankton (mainly cyanobacteria) at low P concentrations. Owing to a lack of apparent resource (P) control, P-management had no detectable effects on phytoplankton biomass. The trophic structures identified in the lake provides explanations for this lack of response to P-management and for the differences between the responses of the South Basin of Lake Lugano and other perialpine lakes. Based on the results, lake restoration practice would benefit from a greater understanding and an increased ability to predict trophic structure within and across lakes.     

Evidence of successful river spawning by lake trout (Salvelinus namaycush) in the Lower Niagara River,Lake Ontario

Restoration of a wild-produced lake trout Salvelinus namaycush population in Lake Ontario has not been successful despite the adult population often meeting or exceeding restoration targets. Lack of high-quality spawning habitat in Lake Ontario is suggested as one impediment to recruitment of wild lake trout, although the quantity and location of spawning habitat is poorly understood. If high-quality spawning habitat is limited in Lake Ontario, lake trout may be using uncommon spawning locations such as rivers. Anecdotal angler accounts point to the Niagara River as a lake trout spawning location. To better understand the potential of the Niagara River as a spawning location, egg and juvenile fish collections were conducted 12–14 river kilometers from the mouth of the Niagara River from 2010 to 2012; and mature female lake trout with surgically implanted acoustic tags were monitored from 2015 to 2019. Genetic analyses confirmed 60% of collected eggs and 93% of collected post-hatch juvenile fish in the Niagara River were lake trout. Tagged female lake trout returned to the Niagara River over consecutive years during the spawning season. The short duration of lake trout presence in the river (mean = 56 days/year) suggests female lake trout use the Niagara River primarily for spawning. Diversity in spawning locations may provide lake trout population’s resilience against environmental variability through a portfolio effect. Improved identification of riverine spawning locations, including their overall contribution to wild recruitment, may be a useful tool for managers to restore a wild-produced population of lake trout in Lake Ontario.     

Temporal dynamics and drivers of lake ecosystem metabolism using high resolution observations in a shallow,tropical, eutrophic lake (Laguna Lake,Philippines)

The physical, chemical, and biological dynamics under changing atmospheric conditions of Laguna Lake, Philippines were analyzed from intensive observations. Diel measurements were conducted for 48 continuous hours for both dry and wet tropical seasons in addition to fine resolution long-term monitoring. Results revealed significant vertical and diel variations of lake variables in spite of a shallow water depth (2.5 m) caused by the intense surface heating from solar irradiance (~800 W m^?2) and accentuated by the lake's high turbidity (16–32 ftu). Late afternoon land-lake breeze (~5–7 m s^?1) regularly breaks daytime thermal stratification, and convective cooling at night maintains isothermal condition until dawn of the next day. The stratified condition demonstrated a wind-driven, density-induced 2-layer current pattern with a windward moving epilimnion (~4 folds faster) and a compensating hypolimnetic flow in the general lake circulation direction. Laguna Lake was observed to have a dominating diel cycle but also undergoes significant seasonal limnological variations brought primarily by climate, hydrology, and its interaction with the adjacent sea. Significantly correlated variations of pH, chlorophyll-a and DO in the dry season were indicative of the higher biological activity associated with the intrusion of polluted waters from Metro Manila. The non-occurrence of thermal over-turn was observed to be regularly followed by bottom hypoxic conditions (2–4 mg L^?1), indicative of the eutrophic condition of the lake and the importance of diel wind-induced mixing in the bottom supply of DO. Laguna Lake was found to be predominantly net heterotrophic (GPP:R < 1, NEP < 0).     

Seasonal variation in the phytoplankton of a saline lowland river (Buenos Aires,Argentina) throughout an intensive sampling period

The aim of this survey was to analyse seasonal variations in phytoplankton composition and abundance with respect to temperature and conductivity values at two sampling sites in the Salado River's lower basin: El Destino and Guerrero. Samples were taken twice a week from 9 March 2004 to 20 July 2004. A total of 145 and 143 species were identified for these two sites, respectively. Infrequent species were discarded to avoid statistical misinterpretations. Autocorrelation analyses (Ljung‐Box Q‐statistic) were performed in order to establish seasonal patterns for species abundance. Similar significant (p < 0.05) autocorrelation patterns were observed for phytoplankton species composition, temperature and conductivity, thus, illustrating correlations with seasonal behaviour. On the basis of these data, species were grouped as (1) late‐summer: with 34 species well represented in warm waters (>22°C) (e.g. Planctonema lauterbornii and Chroococcus spp.); (2) winter: with 10 species that reached their highest densities in cold waters (<12°C) (e.g. Binuclearia eriensis and Microcystis firma); (3) transitional: of only four species with abundance peaks during intermediate conditions (15.5°C average) such as Closteriopsis acicularis and Nodularia spumigena and (4) independent: with 22 species of random behaviour whose autocorrelations remain within confidence limits. These four classifications pertain to species with similar presence at both sampling sites; the rest of the species evinced slightly different patterns. An apparent season‐associated succession of species was detected with those adapted to the warm, stagnant water of the late summer being replaced by others acclimated to the cold water of the winter. Copyright © 2009 John Wiley & Sons, Ltd.     

黔南州河(湖)长制推行的成效、问题和对策探讨

河(湖)长制是实现生态文明建设的重要方针政策,也是新时期国家水治理体系的机制创新。贵州省黔南布依族苗族自治州积极响应国家号召,通过采取高位推动、制度配套、管理创新等方式,有效推进了河(湖)长制工作,并取得了阶段性成效,但实践中依然存在治理能力不足、生活污水处理设施不完善、农村生活垃圾治理滞后、重点流域污染治理形势严峻、信息化监管能力不足及群众参与度不高等问题。本文对黔南州河(湖)长制工作取得的成效和存在的问题进行了阐述,在此基础上,提出强化责任落实、加快基础设施建设、加强重点流域污染治理、提升信息化监管和加大宣传引导等对策建议,尽快补齐河(湖)长制工作短板,更好地推进生态文明建设进程。     

长江口南支边滩悬沙级配的现场与室内观测结果的比较分析

根据2005年6月在长江口南支边滩的现场悬沙级配观测数据和悬沙水样的室内粒度分析数据,对分散状态与未分散状态下的悬沙级配的时空分布特征、絮团对悬沙级配的影响及其现场含量等进行了研究。室内粒度分析结果表明,在颗粒分散条件下,悬沙组成较细,以粉砂和粘土为主,悬沙级配的时间和空间变化较小;悬沙级配有明显的垂向分布规律,平均粒径等在垂向上呈线性分布。现场观测结果显示,在颗粒未分散条件下,悬沙组成较粗,粒径大于63μm和4~63μm的颗粒是悬沙的主要成分,悬沙级配在潮周期内变化显著。对比表明,悬沙级配的现场与室内观测结果差异显著,前者明显粗于后者,絮凝作用是造成差异的主因,絮团在现场悬沙中的含量估计超过60%,絮凝作用能够使参加和不参加絮凝作用的泥沙颗粒在絮凝前、后的体积含量发生明显改变。絮团与流速和悬沙浓度的关系复杂,在潮周期内的部分时段里,悬沙平均粒径与流速和悬沙浓度存在较好的线性关系。     

Impact of light regimen and self-shading by algal cells on primary productivity in the water column of a shallow tropical lake (Lake Naivasha, Kenya)

Light is the factor that fundamentally determines the level of primary production. Primary productivity is controlled by bottom‐up factors (nutrient levels), with secondary effects due to biological factors (zooplankton grazing). The light regimen experienced by algae is determined largely by mixing of the water column. The processes of photoinhibition and light attenuation combine with the resultant light–dark adaptation to shape the vertical productivity profile and it is important to determine their importance separately because they vary spatially and temporally. Daily variations in productivity can be as large as longer‐term changes and events causing high productivity may not be important in whole‐lake terms. At approximately 0.5 m depth, there is maximal photosynthesis causing depletion of nutrients, but there is vertical homogeneity in productivity control and horizontal similarity in productivity levels. There is zero productivity below 5 m depth due to light attenuation but, if the benthos becomes productive due to an environmental change, such as decreased turbidity, overall productivity may rise appreciably. Self‐shading was investigated by incubating serial dilutions of whole lakewater with filtered water to reduce the density of algal cells. Photosynthetic efficiency was calculated as productivity per unit of chlorophyll a. Self‐shading showed different responses for conditions of ‘low’ and ‘high’ productivity. With low productivity, there was a shading loss of 17%, while for high productivity this was 46%. Thus, self‐shading is seen to have a considerable impact on potential productivity and may affect phytoplankton–cyanobacterial community structure with implications for lake management.     

Evidence of lake trout (Salvelinus namaycush) spawning and spawning habitat use in the Dog River,Lake Superior

Lake trout spawn primarily in lakes, and the few river-spawning populations that were known in Lake Superior were believed to be extirpated. We confirmed spawning by lake trout in the Dog River, Ontario, during 2013–2016 by the collection of and genetic identification of eggs, and we describe spawning meso- and microhabitat use by spawning fish. Between 2013 and 2016, a total of 277 lake trout eggs were collected from 39 of 137 sampling locations in the river. The majority of eggs (220) were collected at the transition between the estuary and the river channel crossing the beach. Lake trout eggs were most often located near the downstream end of pools in areas characterized by rapid changes in depth or slope, coarse substrates, and increased water velocities, where interstitial flows may occur. Depths in wadeable areas where eggs were found averaged 0.9?m (range: 0.4 to 1.3?m) and substrate sizes consisted of large gravel, cobble, and boulder; comparable to spawning characteristics noted in lakes. Water velocities averaged 0.66?m·s^?1 (range: 0.33 to 1.7?m³·s^?1) at mid-depth. This information on spawning habitat could be used to help locate other remnant river-spawning populations and to restore river-spawning lake trout and their habitat in rivers that previously supported lake trout in Lake Superior. The Dog River population offers a unique opportunity to understand the ecology of a river spawning lake trout population.     

Occurrence of residues of veterinary antibiotics in water,sediment and trout tissue (Oncorhynchus mykiss) in the southern area of Lake Titicaca,Peru

The city of Puno in Peru is the largest producer of trout (Oncorhynchus mykiss) using intensive floating cage systems installed in Lake Titicaca. As a result, the increase in diseases and the use of antibiotics to control them during the production cycle has been documented. We study the impact of antibiotics on drinking water, trout tissues and the lake's aquatic ecosystem. Nine antibiotics were monitored: tetracyclines, sulfonamides and fluoroquinolones. The samples were collected randomly and analyzed by liquid chromatography coupled to mass spectrometry and the solid-phase extraction system. The sediment samples and surface water samples contain high concentrations of antibiotics. All sediments contain fluoroquinolones (3.74 mg kg^?1) and tetracyclines (3.08 mg kg^?1) and the surface water contains fluoroquinolones of up to 408.2 and 652.7 ng L^?1 in the dry and rainy seasons respectively (P > 0.05). Drinking water samples from the city of Puno collected at sampling points with Lake Titicaca as a source of drinking water, reached an average of 188.1 and 222.2 ng L^?1 of ciprofloxacin in dry and rainy seasons respectively. Complementarily, in trout tissues, it reached 7.8 μg kg^?1 in oxytetracycline 8.7 μg kg^?1 in sulfatizole, 4.2 μg kg^?1 in ciprofloxacin and 3.6 μg kg^?1 in sarafloxacin. The presence of these antibiotics in surface water is attributed to the aquaculture activity, in addition to runoff and wastewater, and their presence can have detrimental effects on the aquatic ecosystem, and even affect public health due to the consumption of aquaculture products and drinking water contaminated with antibiotic residues.     

Channel response to sediment replenishment in a large gravel‐bed river: The case of the Saint‐Sauveur dam in the Buëch River (Southern Alps,France)

The Saint‐Sauveur dam was built in 1992 in the middle section of the Buëch River. Downstream of the dam, a channel incision by several meters was observed. A gravel replenishment operation was planned in order to restore the active channel. An equivalent of two times the mean annual bedload‐transport capacity (43,500 m³) was replenished downstream of the dam in September 2016. The aim of this paper is to quantify morphological change associated with sediment remobilization in order to evaluate the efficiency of the restoration works. The monitoring was based on a combination of (a) change detection using sequential high‐resolution digital elevation models (from airborne LiDAR data), (b) bedload tracing using active ultrahigh‐frequency radio‐frequency identification technology, and (c) complementary field surveys of channel grain‐size distribution and morphology for bedload‐transport computation. Field monitoring allows us to capture a net aggradation along a 2‐km reach after the first post‐replenishment flood. A sediment balance analysis was performed to back‐calculate bedload supply coming from the sluicing operation during the flood. Although the sediment replenishment operation clearly had a positive impact on the morphological conditions of the starved river reach, the effective bedload supply from artificial berms (22,650 m³) was insufficient to initiate substantial channel shifting along the restored reach and a subsequent amplification of the sediment recharge. The combination of high‐resolution topographic resurveys and sediment tracing was successful to evaluate the downstream propagation of sediment replenishment effects.     

Dynamics of the relative nitrogen and phosphorus concentrations in a reservoir situated in a semi-arid zone (Sahela,Morocco)

Fluctuations in total nitrogen and phosphorus concentrations and in the N/P ratio (i.e. in terms of mass) were measured at the entry and exit of the Sahela Reservoir (Morocco) throughout an annual cycle. Particulate N and P concentrations in sedimenting particles in the reservoir itself were also measured. The results obtained showed that the spring floods were a major source of N and P inputs, this being especially pronounced for phosphorus that was present mainly in particulate form. In all the compartments of the reservoir analysed, the N/P ratios were high (means between 81 and 314), especially in summer (the only season when the reservoir was emptied) when the supply of P was apparently limited by the drought. However, the values of this ratio in the sedimenting particles remained lower (mean = 21), at levels characteristic of natural communities. This implies that the reservoir's biological communities preferentially store phosphorus, no doubt to maximise their activity in an environment where a large proportion of this element is not bioavailable. Furthermore, it appeared that the quantity of particulate N and P sequestrated by the sediments and the total quantities of N and P leaving the reservoir were greater than the inputs of these nutrients, underlining the importance of lateral and internal nutrient supplies. One spot measurement, made in a single month, showed that nutrient release activity from the sediments was in fact quite considerable.     

Changes in fish communities of the Phongolo floodplain,Zululand (South Africa) before,during and after a severe drought

The Pongolapoort Dam in Zululand, South Africa has regulated the flow of the Phongolo River to its floodplain downstream since 1970. Ecological surveys of the floodplain fish communities were conducted before (1974–6), during (September 1983) and after (August 1984) a severe drought to assess the response of the fish stocks. During the three study periods the floodplain lake communities varied. Fish populations were markedly reduced during the drought. The redistribution offish on the floodplain after the drought was rapid. Colonization of previously dry lakes was mainly by juvenile fish and the mean size of the fish was lower in these lakes than in the refuge lakes. A few species successfully spawned during the drought, although the natural mortality of the young of the year was probably greater due to increased competition and predation in restricted habitats. Large scale spawning in most species occurred immediately after the drought was broken by a large flood.     

Hydrogeochemistry,Isotopic Composition and Water Age in the Hydrologic System of a Large Catchment within a Plain Humid Environment (Argentine Pampas): Quequén Grande River,Argentina

The Quequén Grande River (QGR) is a large catchment (10 000 km²) in the Pampa Plain in Argentina. From November 2004 to April 2013, a hydrochemical and stable isotopes monitoring program was conducted, which included three sampling stations of monthly composite precipitation, weekly samples in two sites along the river and several groundwater samples. A standard data interpretation was initially performed applying standard statistics, Piper diagrams and δ¹⁸O versus δ²H diagrams. The time evolution of the values of δ¹⁸O in precipitation and streamwater were also determined. The integration of hydrogeochemistry and stable isotopes data indicates the existence of three main components of streamflow: (i) baseflow characterized by electrical conductivity (EC) from 1200 to 1800 µs/cm and an isotope composition quite constant around δ¹⁸O ?5.3‰ and δ²H ?33.8‰. Water age for groundwater contribution is typically around 30 to 40 years using chlorofluorocarbons; (ii) direct runoff composed of channel interception and overland flow, which is of low EC in the order of 50 to 100 µs/cm, and a highly variable isotopic composition; and (iii) translatory flow (pre‐event water that is stored within the subsoil) with an intermediate EC and isotopic composition close to that of the weighted average composition of precipitation. The hydrochemical and stable isotopic data allow the differentiation between baseflow and direct runoff. In addition to this, chlorofluorocarbon dating is a useful tool in assessing the dominance of baseflow in a stream. The data lead to a conceptual model in which an intermediate flow system, with mean residence time (MRT) of around 35 years, discharges into the drainage network. A regional flow system (MRT > 50 years) discharges to the ocean. It is concluded that in this large plain catchment streamflow separation, only two components can be applied in: (i) short storm precipitation events having a high sampling frequency and (ii) during long dry periods when pre‐event soil water is not released. Copyright © 2016 John Wiley & Sons, Ltd.