Shallow Freshwater Research Articles

Satellite and airborne remote sensing of gross primary productivity in boreal Alaskan lakes

In terrestrial and marine ecosystems, remote sensing has been used to estimate gross primary productivity (GPP) for decades, but few applications exist for shallow freshwater ecosystems.Here we show field-based GPP correlates with satellite and airborne lake color across a range of optically and limnologically diverse lakes in interior Alaska. A strong relationship between in situ GPP derived from stable oxygen isotopes (δ18O) and space-based lake color from satellites (e.g. Landsat-8, Sentinel-2 and CubeSats) and airborne imagery (AVIRIS-NG) demonstrates the potential power of this technique for improving spatial and temporal monitoring of lake GPP when coupled with additional field validation measurements across different systems. In shallow waters clear enough for sunlight to reach lake bottoms, both submerged vegetation (macrophytes and algae) and phytoplankton likely contribute to GPP. The stable isotopes and remotely sensed shallow lake color used here integrate both components. These results demonstrate the utility of lake color as a feasible means for mapping lake GPP from remote sensing. This novel methodology estimates GPP from remote sensing in shallow lakes by combining field measurements of oxygen isotopes with airborne, satellite and CubeSat imagery. This use of lake color for providing insight into ecological processes of shallow lakes is recommended, especially for remote arctic and boreal landscapes.

Limno-ecological assessment of lentic ecosystems in the western Mediterranean basin (Turkey) using phytoplankton indices.

Great attention has been given to freshwater ecosystems worldwide due to the increased exploitation of water resources and the degradation of water quality. This study was aimed to demonstrate the phytoplankton-stressor interactions using multivariate approaches and assess the ecological conditions of 28 sampling stations of 12 lentic ecosystems (five lakes and seven reservoirs) in the western Mediterranean basin using phytoplankton indices in dry and rainy seasons 2018. Freshwater and brackish water systems were separately ordinated by canonical correspondence analysis. The brackish ecosystems were under pressures of Ar (arsenic), N-N[Formula: see text] (nitrite), Ca (calcium), EC (electrical conductivity), Cl (chloride), B (boron), etc., whereas shallow freshwater ecosystems were associated with total organic carbon. These factors had significant effects on phytoplankton distribution among lentic ecosystems on the basin. Ecological associations of phytoplankton assemblages varied in the western Mediterranean basin during the study. Pseudanabaena catenata and Palatinus apiculatus, considered tolerant taxa, are associated with higher Ar, EC, and V (vanadium) while Desmodesmus abundans and Microcystis flos-aquae are related to total organic carbon. The modified PTI (phytoplankton trophic index) had the highest correlation coefficient value. Scores of the PTI varied from 2.02 in Çavdır Reservoir to 2.59 in Lake Kocagöl. Results of phytoplankton indices indicated that two (Gölhisar and Yazır) lakes and two (Yapraklı and Çavdır) reservoirs were classified as Good, and three lakes and five reservoirs were classified as Moderate condition. Other predicted classifications (high, poor, and bad) by phytoplankton metrics were not represented. The modified PTI could be a suitable phytoplankton metric for assessing the ecological status of lentic ecosystems in the Mediterranean system according to its highest correlation coefficient value. Overall, the results of this limno-ecological study demonstrated that responses of phytoplankton taxa to explanatory factors provide crucial ecological information about their ecology and to estimate the ecological status of lentic ecosystems.

Multiproxy analysis of a Lateglacial-Holocene sedimentary section in the Fuegian steppe (northern Tierra del Fuego, Argentina): Implications for coastal landscape evolution in relation to climatic variability and sea-level fluctuations

We report the sedimentology, palynology, geochemistry, and diatom assemblages of a well-dated succession at Laguna Las Vueltas (LV) on the Atlantic coast of the Fuegian steppe in southern Argentina. The multiproxy analysis offers a unique opportunity to study the evolution of this coastal landscape in relation to past sea level and climate changes in the southern high latitudes. After ca. 19,000 cal yr BP, the sediments were subjected to subaerial exposure and oxidation linked to a low sea level. The Sr/Ba ratio (a paleosalinity geochemical parameter) indicates variations in the water body level, and diatoms imply the existence of an ephemeral and brackish-freshwater body subject to desiccation under arid conditions. Between ca. 11,600 and 8500 cal yr BP, a shrubby steppe vegetation, mainly composed of Asteraceae subf. Asteroideae, spread over the coastal area associated with a shallow freshwater body and the deposition of fine-grained sediments in low-energy environments, all indicative of low effective moisture and warm climate conditions. Between ca. 8500 and 8100 cal yr BP, salt carpet vegetation, dominated by Chenopodiaceae, developed around a coastal lagoon in response to the Holocene marine transgression. The record of dinocysts and geochemical data indicate marine influence at this time. Between ca. 8100 and 7000 cal yr BP, salt marshes colonized the coastal area. A coastal lagoon with a more restricted connection to the sea and minor freshwater input are inferred, linked to the beginning of a regressive phase. After ca. 7000 cal yr BP, grassland vegetation and an open shrub stratum developed along with a shallow lake (pan) that was disconnected from the sea, following a fall in the sea level and regression. Fluctuations in the water level of the pan and changes in the physical-chemical conditions, as indicated by fluctuations in Mn/Fe, Ti/Ca, Rb/Sr, Ca, TIC and TOC, suggest abrupt events of desiccation and flooding. Between ca. 4500 and 2000 cal yr BP a drier phase is indicated by changes in vegetation, algal content and geochemistry of the pan. A grassland vegetation and a shallow lake with seasonal water level variations characterized the last 2000 years. Our results from LLV area match well with Andean forest fluctuations and regional climatic conditions recorded from Tierra del Fuego and Chilean southwest.

Multi-interaction network performance under global change: a shallow ecosystem experimental simulation

Shallow freshwater ecosystems are structurally complex with different, highly-coupled habitats: the pelagic, the within-macrophyte-meadow, and the benthic. Submerged macrophyte meadows support benthic microorganisms and provide the trophic network with non-trophic relationships. Multi-interaction network analysis disentangles how these systems respond to changes in global-change-related factors. We examined whether (i) populations’ responses to such disturbances are habitat-dependent, and (ii) if whole-community configurations are different. We performed an indoor-mesocosm experiment (“control” plus two disturbed scenarios: enhanced ultraviolet radiation (UVR) or temperature), recreating shallow freshwater ecosystems. We assessed the population-nodes’ carbon biomass, their resistance and resilience to the disturbances, and global- and node-scale structural parameters of the multi-interaction network. Under the UVR-scenario, the phytoplankton C-biomass (from pelagic and within-meadow habitats) was significantly the highest, with mixotrophs dominating. Warming favoured macrophyte growth and significantly increased the network’s size and nestedness, with zooplanktonic herbivores playing a connector role. The within-meadow and benthic habitats’ nodes were highly influential for the network, whatever the scenario. The benthic nodes were the most resistant to the disturbances. Therefore, a phytoplankton- and a macrophyte-dominated configuration was attained under UVR and warming scenarios, respectively. The macrophyte meadows, and the community linked to them, were pivotal in the achievement of these contrasting configurations.

Biogeographic patterns of abundant and rare bacterial and microeukaryotic subcommunities in connected freshwater lake zones subjected to different levels of nutrient loading.

To reveal whether the patterns of abundant and rare subcommunity composition of both bacteria and microeukaryotes vary between connected regions with different levels of nutrient loading in freshwater lakes. We investigated the abundant and rare subcommunity composition of both bacteria and microeukaryotes in two connected zones (Meiliang Bay (MLB) and Xukou Bay (XKB)) of a large shallow freshwater Lake Taihu via the high-throughput sequencing of bacterial 16S rRNA and microeukaryotic 18S rRNA genes. Even though these two lake zones are connected and share a species bank, they diverge in community composition. Significantly higher alpha diversity was observed for the abundant bacterial subcommunity in the MLB. However, no significant difference in alpha diversity between the rare bacterial subcommunities, as well as both rare and abundant microeukaryotic subcommunities were observed between MLB and XKB. It is demonstrated that both environmental factors and geographic distance play central roles in controlling the rare and abundant microbial subcommunities in the two connected lake zones. The abundant subcommunity composition of bacteria and microeukaryotes vary between connected regions with different levels of nutrient loading. Dispersal limitation plays a vital role in shaping microbial communities even in connected zones of freshwater lakes. Leading to a comprehensive understanding of the characteristics of microbial community in connected lake regions with different levels of nutrient loading.

The Seminavis robusta genome provides insights into the evolutionary adaptations of benthic diatoms

Benthic diatoms are the main primary producers in shallow freshwater and coastal environments, fulfilling important ecological functions such as nutrient cycling and sediment stabilization. However, little is known about their evolutionary adaptations to these highly structured but heterogeneous environments. Here, we report a reference genome for the marine biofilm-forming diatom Seminavis robusta, showing that gene family expansions are responsible for a quarter of all 36,254 protein-coding genes. Tandem duplications play a key role in extending the repertoire of specific gene functions, including light and oxygen sensing, which are probably central for its adaptation to benthic habitats. Genes differentially expressed during interactions with bacteria are strongly conserved in other benthic diatoms while many species-specific genes are strongly upregulated during sexual reproduction. Combined with re-sequencing data from 48 strains, our results offer insights into the genetic diversity and gene functions in benthic diatoms.

Responses of four submerged macrophytes to freshwater snail density (Radix swinhoei) under clear-water conditions: A mesocosm study.

Macrophytes play a key role in stabilizing clear‐water conditions in shallow freshwater ecosystems. Their populations are maintained by a balance between plant grazing and plant growth. As a freshwater snail commonly found in shallow lakes, Radix swinhoei can affect the growth of submerged macrophytes by removing epiphyton from the surface of aquatic plants and by grazing directly on macrophyte organs. Thus, we conducted a long‐term (11‐month) experiment to explore the effects of snail density on macrophytes with distinctive structures in an outdoor clear‐water mesocosm system (with relatively low total nitrogen (TN, 0.66 ± 0.27 mg/L) and total phosphorus (TP, 36 ± 20 μg/L) and a phytoplankton chlorophyll a (Chla) range of 14.8 ± 4.9 μg/L) based on two different snail densities (low and high) and four macrophyte species treatments (Myriophyllum spicatum, Potamogeton wrightii, P. crispus, and P. oxyphyllus). In the high‐density treatment, snail biomass and abundance (36.5 ± 16.5 g/m2 and 169 ± 92 ind/m2, respectively) were approximately twice that observed in the low‐density treatment, resulting in lower total and aboveground biomass and ramet number in the macrophytes. In addition, plant height and plant volume inhabited (PVI) showed species‐specific responses to snail densities, that is, the height of P. oxyphyllus and PVI of M. spicatum were both higher under low‐density treatment. Thus, compared with low‐density treatment, the inhibitory effects of long‐term high snail density on macrophytes by direct feeding may be greater than the positive effects resulting from epiphyton clearance when under clear‐water conditions with low epiphyton biomass. Thus, under clear‐water conditions, the growth and community composition of submerged macrophytes could be potentially modified by the manual addition of invertebrates (i.e., snails) to lakes if the inhibitory effects from predatory fish are minor.

Succession of sulfur bacteria during decomposition of cyanobacterial bloom biomass in the shallow Lake Nanhu: An ex situ mesocosm study

Previous studies of the dynamics of sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB) have focused on deep stratified lakes. The objective of this study is to present an in-depth investigation of the structure and dynamics of sulfur bacteria (including SRB and SOB) in the water column of shallow freshwater lakes. A cyanobacterial bloom biomass (CBB)-amended mesocosm experiment was conducted in this study, in which water was taken from a shallow eutrophic lake with sulfate levels near 40 mg L−1. Illumina sequencing was used to investigate SRB and SOB species involved in CBB decomposition and the effects of the increases in sulfate input on the water column microbial community structure. The accumulation of dissolved sulfide (∑H2S) produced by SRB during CBB decomposition stimulated the growth of SOB, and ∑H2S was then oxidized back to sulfate by SOB in the water column. Chlorobaculum sequences (the main SOB species in the study) were significantly influenced by increases in sulfate input, with relative abundance increasing approximately four-fold in treatments amended with 40 mg L−1 sulfate (referred to as 40S) when compared to the treatment without additional sulfate addition (referred to as CU). Additionally, an increase in SOB number was observed from day 26–37, concurrent with the decrease in SRB number, indicating the succession of sulfur bacteria. These findings suggest that biological sulfur oxidation and succession of sulfur bacteria occur in the water column during CBB decomposition in shallow freshwater ecosystems, and the increases in sulfate input stimulate microbial sulfur oxidation.

Spatiotemporal changes and drivers of trophic status over three decades in the largest shallow lake in Central Europe, Lake Balaton

The over-enrichment of shallow lakes in nutrients has emerged as one of the main causes of water quality deterioration, and is today a major focus of water quality studies worldwide. In the present work, changes in trophic conditions over three decades (1985–2017) in the largest shallow freshwater lake in Central Europe, Lake Balaton, are assessed using the time series of 10 water quality variables measured at 4 sites, one in each basin of the lake. Using combined cluster and discriminant analyses, and assessing each of the four basins of the lake separately, it was possible to divide the history of the lake into three time intervals. Principal component and Sen's slope analyses highlight the fact that the oligotrophization of the lake took place at a different pace in each of these three major time intervals (1985–1994; 1995–2003; 2004–2017) along the lake's major axis. A significant decrease in the concentration of parameters indicating trophic conditions (e.g. chlorophyll-a, soluble reactive phosphorus) was first observed in the western basins, in the proximity of the main water input to the lake, followed by the eastward spread of this phenomenon. At the same time, the importance of external total phosphorus input to the lake was found to decrease eastwards, thereby diminishing its capacity to explain the variance of the water quality parameters in the lake. Over the time period covered by this study, various measures were taken to reduce the nutrient loads to the lake. These were, in the main, successful, as may be seen in the decade-by-decade overview of the lake's trophic state presented here. A brief review of similar cases from around the world only serves to reinforce the conclusion that a drastic reduction in external phosphorus loads arriving in similar shallow lakes will result in their oligotrophization, albeit with a time-lag of at least ten years.

Tissue concentrations, trophic transfer and human risks of antibiotics in freshwater food web in Lake Taihu, China.

The objective of this study was to evaluate the tissue distributions of antibiotics in the fish, the bioaccumulation and trophic transfer in freshwater food web in Taihu Lake, a large shallow freshwater lake. Twenty four out of 41 antibiotics were detected in the biotas of the food web; and antibiotic concentrations followed the orders: fish plasma~fish muscle<fish liver~fish bile and fish<invertebrates~plankton. Antibiotic concentrations in the liver of piscivores were higher than those in omnivores and planktivores. Most bioaccumulation factors (BAFs) of sulfonamides (SAs), macrolides (MLs), ionophores (IPs) and lincomycin (LIN) were less than 2000 L/kg, indicating low bioaccumulation ability of these compounds in fish. Fluoroquinolones (FQs) were frequently detected in fish liver, invertebrates and plankton with much of BAFs great than 5000L/kg, indicating that FQs have the potential of bioaccumulation in fish. Relationship analysis between BAFs and physicochemical properties of antibiotics showed that the bioaccumulation of antibiotics in the biota was related with their adsorption ability. Generally, the antibiotics in the food web of Lake Taihu including plankton, invertebrates and fish showed trophic dilution. The normalized estimated daily intake (EDI) values are less than the acceptable daily intake (ADI) values, and then hazard quotients were much less than 1. This result suggests the consumption of fish, crab and shrimp in Lake Taihu would probably not pose direct detrimental effects on humans.

The Holocene history of the Faiyum Lake (Egypt) based on sediment characteristics, diatoms and ostracods contents

There are relatively few Holocene lake sediment core sequences available for north-east Africa. This study examines the developmental history of Faiyum Lake (Egypt) by detailed lithostratigraphic description together with microfossils and geochemistry, of two adjacent lake sediment cores. The recovered sedimentary sequence consists of predominantly lacustrine facies divisible into five sedimentary units. Early Holocene sediments (Unit II; c. 9.9–8 ka cal BP), overlying late Pleistocene aeolian sands (Unit I), comprise sub-mm laminations (non-glacial varves) of white diatomite and calcite inter-bedded with yellowish-green mineralogenic layers indicating a deep freshwater lake phase. Early middle Holocene sediments (Unit III, c. 8 to 6 ka cal BP) consists by pockets of non-glacial varved laminae intercalated with turbidites and increasing thick silty clay layers, indicating a shallow freshwater lake phase with increasing nutrients. The late middle Holocene lake phase, Unit IV (c. 6 to 4 ka cal BP) is grey massive mud with occasional thick (>1 cm) diatomite-carbonate layers and thin gypsum and iron-hydroxides layers indicative of a lake shrinking phase but with a large level fluctuation sand evaporation phases when freshwater inflow diminished. The late Holocene lake phase (unit V, c. 4 ka cal BP-present) reveals bioturbation and increasing fine sand with artifacts corresponding to further lake level declines and fluctuations as water management intensifies during and after Middle Kingdom and Ptolemaic times. Together with geochemical and microfossil evidence, sedimentology of the studied cores indicate a series of major environment changes affecting the whole lake system throughout the Holocene.

Climate warming and heat waves alter harmful cyanobacterial blooms along the benthic-pelagic interface.

In addition to a rise in mean air and water temperatures, more frequent and intense extreme climate events (such as heat waves) have been recorded around the globe during the past decades. These environmental changes are projected to intensify further in the future, and we still know little about how they will affect ecological processes driving harmful cyanobacterial bloom formation. Therefore, we conducted a long-term experiment in 400-L shallow freshwater mesocosms, where we evaluated the effects of a constant +4°C increase in mean water temperatures and compared it with a fluctuating warming scenario ranging from 0 to +8°C (i.e., including heat waves) but with the same +4°C long-term elevation in mean water temperatures. We focused on investigating not only warming effects on cyanobacterial pelagic dynamics (phenology and biomass levels), but also on their recruitment from sediments-which are a fundamental part of their life history for which the response to warming remains largely unexplored. Our results demonstrate that (1) a warmer environment not only induces a seasonal advancement and boosts biomass levels of specific cyanobacterial species in the pelagic environment, but also increases their recruitment rates from the sediments, and (2) these species-specific benthic and pelagic processes respond differently depending on whether climate warming is expressed only as an increase in mean water temperatures or, in addition, through an increased warming variability (including heat waves). These results are important because they show, for the first time, that climate warming can affect cyanobacterial dynamics at different life-history stages, all the way from benthic recruitment up to their establishment in the pelagic community. Furthermore, it also highlights that both cyanobacterial benthic recruitment and pelagic biomass dynamics may be different as a result of changes in the variability of warming conditions. We argue that these findings are a critical first step to further our understanding of the relative importance of increased recruitment rates for harmful cyanobacterial bloom formation under different climate change scenarios.

Groundwater mixing in a heterogeneous multilayer aquifer driven by geogenic CO2 fluxes: Evidence from chemical and isotopic composition of Ferrarelle waters (Riardo Plain, southern Italy)

The successful management of carbon in the Earth's crust is critical for mitigating the increase of anthropogenic CO2 in the atmosphere. Carbon Capture and Storage (CCS) requires an understanding of the behavior of carbon in the crust and the development of robust monitoring techniques to constrain the movement, mechanisms, and pathways for any potential CO2 leakage. Here, we examine an aquifer from the Riardo Plain (Campania Region, southern Italy), which serves as a suitable natural analogue for CO2 migration to the critical zone (i.e., shallow crust and aquifers) and as a case study to evaluate the geochemical processes that occur when CO2-saturated fluids mix with freshwater in shallow aquifers. We investigate the behavior of various geochemical constituents (major and trace elements, δ18O–H2O, δ13C-DIC, and Rn content). Water from this area has a high degree of mineralization (EC 2500–3000 μS/cm), high HCO3- (~2.5 g/L), is saturated with respect to CaCO3, and is enriched in alkali ions (e.g., Na+ + K+). The high degree of mineralization occurs in groundwater that discharges from the basal aquifer of the Roccamonfina volcanic edifice (~6 km NW), with vast CO2 inputs that promote host rock leaching. Superficial volcanic aquifers are recharged by fresh meteoric precipitation when groundwater flows from carbonates at the edge of the plain to aquifers hosted in the southeastern slope of the Roccamonfina volcano. The presence of normal faults in this area permits natural upwelling of CO2-rich groundwater, which locally mixes with shallow freshwater present within the upper volcanic succession. Significant (R > 0.8) linear correlations between conservative elements suggest that groundwater geochemistry is dominated by a mixture of two main endmembers: (i) deep/mineralized waters and (ii) shallow/diluted waters. The intrusion of freshwater to volcanic aquifers induces oxidation, leading to adsorption of select elements (e.g., As and Ba) onto Fe-oxyhydroxide precipitates within these aquifers. Geochemical modeling suggests that CO2 saturation approaches 3 g/L, which agrees with direct measurements of CO2 flux. We conclude that our conceptual geochemical model helps to constrain mixing of CO2 with freshwater and to diagnose the secondary geochemical processes that influence aqueous geochemistry within CO2-influenced groundwater.

Gas well integrity and methane migration: evaluation of published evidence during shale-gas development in the USA

More than 1 million wells may have been completed using hydraulic fracturing techniques in the USA alone; however, there have been few case studies exploring the impacts on water resources due to methane migration. This study evaluated the results of three investigations initiated by the US Environmental Protection Agency, that were subsequently described in published studies at Dimock in Pennsylvania, Parker-Hood County in Texas, and Pavillion in Wyoming, as well as another study completed at Sugar Run in northeast Pennsylvania. In addition, earlier investigations at Shaws Corner in Pennsylvania, Jackson County in West Virginia, Garfield County in Colorado, and Bainbridge in Ohio are summarized. The most common cause of incidents was the presence of uncemented sections of production casings in wells that allowed gas migration from intermediate depths to shallow freshwater aquifers. In three cases, an inadequate depth of the primary top of cement (TOC) also contributed to impacts. Sources of methane were best identified through analyses of isotopes on samples from production casings, annular spaces, and water wells. In Dimock, some isotope signatures changed with time, after the completion of remedial actions. In Parker-Hood County, where impacts were not related to gas well activity, noble gas analyses were also needed to determine the source of gas. At Pavillion, where maximum methane concentrations in water wells were <1 mg/L, no significant impacts were documented. For all the sites, most or all of the fugitive gas incidents may have been prevented by fully cementing production casings to the land surface.

Draft Genome Sequence of Raphidiopsis raciborskii Strain GIHE 2018, Isolated from a Shallow Freshwater Pond in South Korea.

The draft genome sequence of Raphidiopsis (Cylindrospermopsis) raciborskii strain GIHE 2018, a filamentous nitrogen-fixing and potentially harmful cyanobacterium, is reported here. This is the first strain isolated from a shallow freshwater pond in South Korea. This information is expected to improve our understanding of the phylogeography of this species.

Utilizing the Geophysical and Hydrogeological Data for the Assessment of the Groundwater Occurrences in Gallaba Plain, Western Desert, Egypt

The investigated region is located in the western desert fringes of the Nile Valley which requires studies of groundwater related to the many projects of land reclamation. The key objective of this paper is to estimate the qualitative and geometrical features of the investigated aquifer. Using 60 vertical electrical sounding and time-domain electromagnetic soundings allows us to suggest one possible model of the geometrical features of the local aquifer. A hydrogeological monitoring has been undertaken to investigate the current groundwater situation at the Gallaba plain. Such hydrological monitoring has not been undertaken before in detail. The results show that the investigated region has high groundwater potentialities in two main aquifers which belong to Pleistocene: shallow fresh water and deep brackish water. The lithological and structural elements contribute mainly to recharge and store the groundwater in the western part of the River Nile in Kom Ombo graben. The geochemical properties of the groundwater of the studied aquifers reflect meteoric water, which is a fresh to slightly brackish water. The small amount of groundwater salinity arises from silicate weathering and evaporation processes occurring in the aquifer matrix. Moreover, most of the studied groundwater samples are unfit for human consumption. Such samples are very satisfactory for livestock and poultry purposes and they can be used for irrigation using modern and improved irrigation methods e.g. sprinkler and drip methods. Furthermore, the hydrogeological monitoring of the concerned area indicates that it has high groundwater potentialities which will support its sustainable development.

Effects of environmental change on subfossil Cladocera in the subtropical shallow freshwater East Taihu Lake, China

East Taihu Lake (the south-eastern portion of Taihu Lake in China) suffers from eutrophication. The study of lacustrine subfossil zooplankton assemblages can be used to reconstruct the long-term evolution of lake water environments. In particular, the analysis of subfossil Cladocera can indicate historical changes in aquaticplants, water level, trophic states, and human disturbance in lakes. In this study, we correlated downcores changes in cladoceran assemblages with several geochemical proxies to identify the response of Cladocera to environmental change in East Taihu Lake over the past one hundred years. Redundancy analysis (RDA) and Pearson correlation analysis identified significant correlations between total phosphorus (TP) and Bosmina spp. (total), B. (E.) longispina, and Chydorus cf. sphaericus (correlation coefficients: −0.720 (P < 0.01), −0.646, and 0.667 (P < 0.05), respectively). We observed decreasing abundances of subfossil Bosminidae and increases in littoral cladoceran species and TP after the 1960s, coinciding with the introduction of land reclamation for fish and crab farming. These anthropogenic pressures exacerbated eutrophication, which led to the rapid growth of submerged vegetation and subsequently altered the zooplankton assemblage.

Water quality influence the phytoplankton and bacteria abundance: a comparison between shallow freshwater and saltwater ponds

Study for understanding the role of various water quality parameters on phytoplankton and bacteria density in shallow freshwater and saltwater ponds is lacking. Therefore, the present study was conducted to understand the difference in influence of various water quality parameters on phytoplankton and bacteria density in freshwater and saltwater ponds. A series of water quality parameters, phytoplankton biomass (as indexed by chlorophyll-a), the density of bacteria and trophic state (as indexed by TRIX index) were determined monthly in two freshwater and two saltwater ponds located in Kuantan, Pahang, Malaysia. Apart from pond type and temporal effects, multivariate ordinations were performed using two different datasets: water quality, and phytoplankton and benthic macroinvertebrates. Water temperature, salinity, and the concentration of TSS and ammonia were significantly (p 0.05) throughout the study period in both freshwater and saltwater ponds. All ponds under study are oligotrophic. In all ponds, the water quality dataset explained the overall variation in phytoplankton and bacteria abundance quite well. Phytoplankton biomass in freshwater ponds is greatly related with phosphate and slightly related with ammonia and water depth. In saltwater ponds, nitrogenous nutrients (nitrate and ammonia) were strong predictors of phytoplankton biomass and stronger than salinity, TSS and pH. Turbidity was the strongest predictor of bacteria density in freshwater and saltwater ponds. It had strong negative influences on bacteria density in freshwater ponds whereas, it had strong negative influences on bacteria density in saltwater ponds. The results of this study support and emphasize the importance for developing appropriate programs for the monitoring and conservation of various freshwater and saltwater ponds.

Analysis of Internal Nutrient Load Dynamics from the Sediment in Lake Ziway

Lake Ziway is shallow freshwater located in Northern part of Ethiopian Rift Valley. Expansions of the flower industry, widespread fisheries, intensive agricultural activities, fast population growth lead to deterioration of both water and sediment qualities and depletion of aquatic biota. The main objective of this study is to evaluate the internal nutrient load dynamics from the sediment. Nutrients in sediment samples were analyzed according to the standard procedures outlined in EPA, 1994 and phosphorus release rate were estimated with THE methods described in Steinman, et al. [3]. The results of sediment depth profile analyses showed that the mean concentrations of SRP, TP, NO3-N, NO2-N and TN were 27.7, 62, 5.28, 8.51 and 1733 mg/kg, respectively in dry season, and 21.2, 73, 7.99, 28.4, 24.2 and 1750 mg/kg, respectively in wet season. The values for all the studied nutrients distribution were higher at sediment top surface and decline with depth of the sediment profiles in most of the sampling sites and seasons. The results of the seasonal evaluation of phosphorus flux from lake sediments showed that sediments were sources of phosphorus. The findings from the current study indicate that internal sources of nutrients to Lake Ziway vary across time and space. Understanding this variation and internal nutrient load is important in developing mitigation and restoration strategies for the lake ecosystems.

Decomposition in flocculent sediments of shallow freshwaters and its sensitivity to warming

Shallow waterbodies are abundant in many landscapes across the globe and are increasingly acknowledged for their role in freshwater C cycling. This study investigated organic-matter decomposition potentials in flocculent organic sediment, a rarely-investigated sediment type commonly found in shallow waters. Further, this study investigated how porewater chemistry and temperature affect decomposition rates within flocculent sediment. We quantified decomposition rates during 3 seasons by deploying a standardized substrate (cotton strips) within and above the flocculent sediment layer in the littoral zones of lakes, shallow through-flow wetlands, and depositional zones on the margins of stream channels of southwestern Michigan, USA. We then compared our results with those reported for other freshwater settings that used the same cotton-strip assay. There was high accumulation of organic matter in the shallow waterbodies, but decomposition rates in flocculent sediments averaged 1.7× greater than rates measured in oxic overlying waters and were generally only eclipsed by temperature-adjusted rates reported in streams, which are typically well-oxygenated, flowing environments. Rates were positively correlated with sediment porewater concentrations of soluble reactive P and dissolved iron and negatively correlated with ammonium. Warmer temperatures also resulted in increased decomposition rates, and the temperature sensitivity results suggest that decomposition rates in flocculent sediments could increase 11 to 52% with a 1 to 4°C increase in water temperatures, a realistic range of increase for this region in the next 100 y if climate change continues at the current pace. Thus, high organic matter inputs, rather than slow decomposition, must lead to the development of flocculent organic sediments. Future warming could therefore increase decomposition rates and tip the balance toward net losses of organic matter.