Coastal Reservoirs Research Articles

Stochastic processes driving cyanobacterial temporal succession in response to typhoons in a coastal reservoir

Typhoons associated with heavy rainfall events, potentially triggering harmful algal blooms (cyanoHABs) dominated by cyanobacteria in coastal reservoirs. These blooms deteriorate water quality and produce toxins, posing a threat to aquatic ecosystems. However, the ecological mechanisms driving cyanobacteria communities in response to typhoons remain unclear. To address this gap, we investigated a coastal reservoir with high-frequency sampling during two typhoon seasons. We employed comprehensive statistical methods under neutral and evolutionary theories to analyze environmental dynamics and cyanobacterial genus succession. Our findings revealed a significant increase in nutrient loads following typhoons, with concentrations of total nitrogen (TN), total phosphorus (TP), and ammonia-nitrogen (NH4+-N) rising from 0.4 mg/L to 1.0 mg/L, 0.02 mg/L to 0.63 mg/L, and 0.03 mg/L to 0.26 mg/L, respectively. These changes coincided with fluctuations in other physicochemical parameters under changing hydrometeorological conditions. Despite significant environmental disturbances, the cyanobacterial community exhibited a remarkable recovery within 15–25 days following the typhoons. This recovery progressed through four distinct successional phases, with a notable shift in community composition from Raphidiopsis and Pseudoanabaena to Aphanocapsa, subsequently replaced by Raphidiopsis and Microcystis, before reverting to the pre-typhoon community structure. During the entire successional phase, the availability of TN and the TN/TP ratio played a dominant role, as indicated by PLS-PM analysis (total effects = -0.6; p < 0.05). Pre-typhoon, environmental factors primarily influenced community structure (54 %) based on modified stochasticity ratio. However, following the typhoons, stochastic fluctuations took precedence (71 %-91 %). The rapid recovery of cyanobacterial communities and the shift in driving mechanisms from deterministic to stochastic processes underscore the complex ecological responses to typhoon events. This study provides essential insights for biodiversity preservation and ecosystem restoration, emphasizing the need to consider both stochastic and deterministic processes in ecological management strategies.

Assessment of Sensitivity and Validity Hydrodynamic Model in Cisadane Using Delft3d Flow Model

The National Capital Integrated Coastal Development (NCICD) program was prioritized as a disaster reduction technology within the annual target of BRIN in 2022. It is a part of the North Java Coastal Integrated Development Program project. A coastal reservoir development plan at the Cisadane River estuary is one of the outcomes. In this case, hydrodynamic modelling is needed to acquire hydrodynamic properties under the existing condition of Cisadane downstream, and it applied the Delft3D-FLOW model. The bathymetric data used in this simulation was obtained from the assimilation of national bathymetric data with a grid spacing of 180 m and field survey data with a horizontal resolution of 10 m and transect spacing of 200 m seaward of the Cisadane estuary. It has interpolated in a regular structured grid with 100 m and 50 m grid spacing. In addition, other data used are three hourly wind data downloaded from the European Centre for Medium-Range Weather Forecasts (ECMWF) and the daily discharge of the Cisadane River in 2021. Astronomical water level data generated from TPXO 7.2 and TPXO 8 were used in the boundary conditions. These data are simulated using the two and three-dimensional flow model Delft3D-FLOW during November 1 – 15, 2021, using four manning coefficients (n) values, which are 0.03; 0.035; 0.04; and 0.045. The validation formulation used Normalization Root Mean Square Error (NRMSE), resulting in 5.3 - 9.6% for all the manning values and domains. The highest correlation coefficient of current velocity (u-v components) is acquired in the 10 km2 domain with 0.797 for the L3 (bottom layer).

Food webs in isolation: The food-web structure of a freshwater reservoir with armoured shores in a former coastal bay area

Many shallow coastal bays have been closed off from the sea to mitigate the risk of flooding, resulting in coastal reservoir lakes with artificial armoured shorelines. Often these enclosed ecosystems show a persistent decline in biodiversity and ecosystem services, which is likely reflected in their food-web structure. We therefore hypothesize that the food webs of coastal reservoir lakes with armoured shorelines (1) consist of relatively few species with a low food-web connectance and short food chains, and (2) are mainly fuelled by autochthonous organic matter produced in the pelagic zone. To investigate these two hypotheses, we used stable-isotope analysis to determine the food-web structure of lake Markermeer (The Netherlands), a large reservoir lake with armoured shorelines in a former coastal bay area. Contrary to expectation, connectance of the food web in lake Markermeer was comparable to other lakes, while food-chain length was in the higher range. However, the trophic links revealed that numerous macroinvertebrates and fish species in this constructed lake exhibited omnivorous feeding behaviour. Furthermore, in line with our second hypothesis, primary consumers heavily relied on pelagically derived organic matter, while benthic primary production exerted only a minor and seasonal influence on higher trophic levels. Stable-isotope values and the C:N ratio of sediment organic matter in the lake also aligned more closely with phytoplankton than with benthic primary producers. Moreover, terrestrial subsidies of organic matter were virtually absent in lake Markermeer. These findings support the notion that isolation of the lake through shore armouring and the lack of littoral habitats in combination with persistent resuspension of sediments have affected the food web. We argue that restoration initiatives should prioritize the establishment of land-water transition zones, thereby enhancing habitat diversity, benthic primary production, and the inflow of external organic matter while preserving pelagic primary production.

A Methodology for Water Resource Management and the Planning of the Coastal Reservoir in Indonesia

Metropolitan areas in Indonesia, specifically Jabodetabek, are projected to continue experiencing population growth. This will result in increased water demand, which, if left unchecked, could lead to a water crisis. Additionally, the region faces persistent flooding issues. To mitigate these challenges, the Indonesian government proposes the creation of a coastal reservoir. However, a methodology for the pre-feasibility study of such reservoirs in Indonesia is currently lacking. This study addresses this gap by presenting a methodological framework encompassing hydrology and water allocation analyses as well as numerical modeling related to hydraulic and sedimentation aspects of coastal reservoirs. The methodology was designed to be adaptable based on data availability. Finally, this methodology was applied to a case study located at the Cisadane River estuary. The water allocation simulation showed that the reservoir can release an annual optimum discharge of 80.618 m3/s in wet years and 22.731 m3/s in dry years. Flood modeling demonstrated a modest impact on reducing early-hour floods, with a water level decrease of around 20–50 cm within 5 km of the reservoir. Furthermore, sediment modeling revealed varying sedimentation and erosion depths along the rivers, with approximately 62,300 m3/year settling in the reservoir.

Distribution of Algae According to Habitat Preferences in Saline Coastal Reservoirs of Pryazov National Natural Park (Ukraine)

This study focused on the distribution of algae in the saline coastal water bodies of Pryazov National Nature Park according to their habitat preferences. This research revealed that aquatic species form the basis of the algal flora. Among these, diatoms were predominant in terms of species richness and frequency of occurrence. In the lake-type estuaries and ephemeral water bodies, an increased number of amphibious species were found, which can be attributed to the fluctuating water level. Among the amphibious species, &lt;i&gt;Cyanoprokaryota&lt;/i&gt; representatives dominate. Hierarchical clustering of the water bodies demonstrated a connection between the species composition of algae and the type of water body, which is consistent with their genesis and transformation.

Seepage Analysis and the Reservoir Water Pollution Potential under Vertical Dam Structure Planning

A prospective resolution to the intricate predicaments of flooding, sanitation, and the availability of unprocessed water for the populace of Jakarta residents is the implementation of the coastal reservoir paradigm. This paradigm entails harnessing the latent capacity of the Cisadane River flow and its subsequent storage within a retention pond, and then subjecting it to reprocessing to serve as a viable source of raw water. The selection of a vertical seawall design was based on the objective of creating an effective barrier between the reservoir and the sea, while also considering several environmental factors. This design was selected with the aim of minimizing the need for extensive soil excavation and rock placement. However, it is important to note that the risks of construction failure associated with seepage under hydraulic structure and dam stability pose significant challenges. Besides preventing saltwater intrusion and maintaining the integrity of the reservoir as a freshwater source, dam must be designed to mitigate potential seepage failure and intrusion issues. To address these concerns, this study employed numerical simulation using the SEEP/W and CTRAN/W software. The simulation was carried out to analyze seepage discharge under a vertical dam and predict potential seawater intrusion into the reservoir. The dam was examined over a ten-year period, with varying embankment widths of 10m, 20m, and 30m. The analysis considered changes in water level (ΔH) and the addition of a cut-off wall at depths of 5m, 10m, and 15m. The obtained results showed that seepage discharge rates amounted to 3,14x10-4 m3 s-1, 2,67x10-4 m3 s-1, and 2,50x10-4 m3 s-1 for embankment widths of 10m, 20m, and 30m, respectively, under a 1m level difference condition. Following this, the safety factor for piping on vertical embankment was determined as 1.10, 1.34, and 1.39 for widths of 10m, 20m, and 30m, respectively. This factor was found to increase to 4.03 when the embankment distance was widened, and a 15m deep cut-off wall was installed. It is important to note that the seawater intrusion model predicted a seawater concentration of 65,12 g m-3 at the bottom for an embankment width of 10m, while no intrusion was observed at widths of 20m and 30m with ΔH=1m. This study aims to assess potential risks of piping due to seepage and seawater contamination at the Cisadane Estuary.&#x0D;

Using Coastal Reservoirs for a Sustainable Freshwater Supply: Feasibility Study in Ningbo, China

Using Coastal Reservoirs for a Sustainable Freshwater Supply: Feasibility Study in Ningbo, China

Multipurpose Freshwater Coastal Reservoirs and Their Role in Mitigating Climate Change

A coastal reservoir (CR) is a freshwater reservoir to store river water in the sea area adjacent to the sea coast by replacing seawater. A CR is formed by constructing a long oceanic dike to impound surplus water that is flowing to the sea from a river basin. Freshwater from the CR is pumped throughout the year into a series of embankment canals to reach upland areas for meeting agricultural, industrial, municipal, etc water needs along with the required base blows and environmental flows in river basins. The embankment canals also create pumped storage hydropower (PSHP) potential to meet the energy storage requirements for harnessing variable power resources like solar, wind, etc which are economical, clean, renewable, and carbon neutral. The oceanic dike also creates a mega-scale ultra-deep sea harbor along with a coastal highway and railroad. CRs are cheaper to construct compared to land-based reservoirs wherever the cost of submerged land and immovable property acquisition and rehabilitation of the affected population is very high. They also serve multipurpose utilities such as deep-sea harbor, road transport, rail transport, land reclamation, PSHP energy storage, rejuvenation of over-exploited rivers, etc without appreciable overall environmental damage. CR projects are feasible in every continent except Antarctica as there are few mighty rivers with huge surplus water discharges to the sea and also the existence of vast desert/semi-desert areas which can be converted into productive agricultural lands or forest lands with water supplied from the CRs. Greening the desert or semi-desert lands into lush green farms or forest lands would enhance the soil carbon storage and also provide food grains and biomass. The available biomass can be used as feedstock to produce carbon-neutral biofuels to replace fossil fuels which are contributing to global warming. Few feasible CR projects are listed in the paper that can harness nearly 9,000 billion cubic meters (bcm) of water annually and contribute to achieving a carbon-neutral world. To explain the concept of the freshwater CRs and the associated embankment canals, a CR project to utilize the surplus waters of the Brahmaputra, Ganga, and Meghna rivers is considered as a case study in some detail in this paper. The project would create a 360 bcm capacity CR to harness nearly 1,200 bcm of water throughout the year regardless of monsoon vagaries for meeting various water needs in all major river basins between the Ganga and Krishna rivers.

Hydrodynamic modelling and shape optimisation of second-generation coastal reservoirs in consideration of algal bloom occurrence

Algal bloom has been a persistent problem for both fresh and marine water, with no exception for a coastal reservoir (CR). Among the algal bloom mitigations for a CR, shape optimisation to reduce algal bloom occurrence has been frequently mentioned. However, there was no literature found on the actual shape optimisation study or process for CR. Thus, this research was done to bridge this gap, particularly for the second-generation CR. Hydrodynamic model of MIKE 21 has been used, with secondary data obtained from published papers and Google Earth. The secondary data of critical velocity corresponding to algal growth were only available for cyanobacteria, chlorella, filamentous algae and phytoplankton. Hence, only these algae species were considered in the algal mapping. All models were simulated for eight idealised cases of second-generation CR at the Yangtze Estuary. These different geometric shapes were analysed and compared, considering several factors including the average velocity in the reservoir, presence of stagnant water, percentage of occurrence for each algae species and so on. From the results, the reservoir model with the shape of “shorter piano key” ranked the highest among all the shapes in terms of proneness to algal bloom, based on the flow velocity within the reservoir. From the findings, further shape optimisation was done on second-generation CRs. From shape optimisation process, the optimised shape of the “little dinosaur” and “little pencil” showed excellent reduction in algal blooming. However, “little dinosaur” was preferred as its location for algal bloom is small and controllable due to the presence of “piano key” structure. Lastly, all the findings were applied to an existing CR at Qingcaosha to see if shape optimisation based on the analysis can reduce areas prone to algal blooming. The optimised model of Qingcaosha showed great reduction on area prone to algal blooming compared to its original shape but the addition of “piano key” structure did not have significant impact on the reduction of algal bloom occurrence since the shape of Qingcaosha is highly dependent on its natural topography. From the study, it was concluded that shape optimisation for topographic-dependent CR should be done on case-by-case basis, following the flow direction in the reservoir. As for second-generation CR without topographical constraints, the shape optimisation can be done by placing inlet perpendicular to the flow direction, minimising corners, implementing piano-key-like structure, optimising shape based on flow direction and refer “little dinosaur” or “little pencil” for the overall shape optimisation design.

Cuspidothrix Is the First Genetically Proved Anatoxin A Producer in Bulgarian Lakes and Reservoirs.

The paper presents the first proof of planktonic cyanoprokaryote genus Cuspidothrix as an anatoxin A (ATX) producer in Bulgarian wetlands. The results from polymerase chain reaction (PCR) obtained from two summer sampling campaigns in 26 selected lakes and reservoirs demonstrated presence of the anaC gene, responsible for ATX production in 21 strains of the genus. They were found in three waterbodies sampled in 2018 (coastal lake Vaya, coastal reservoir Poroy, inland reservoir Sinyata Reka) and in four waterbodies sampled in 2019 (inland reservoirs Duvanli, Koprinka, Plachidol 2, Sinyata Reka). The detected genetic diversity generally corresponds to the observations conducted by conventional light microscopy, by which we distinguished three species of Cuspidothrix (Cuspidothrix issatschenkoi, Cuspidothrix elenkinii and Cuspidothrix tropicalis, the latter considered alien in the country). Eleven strains showed high similarity to two sequences of C. issatschenkoi available from the National Centre for Biotechnology Information (NCBI). Ten other strains assembled in a group, which-in lack of available from NCBI genetic sequences-were presumed related to C. tropicalis and C. elenkinii after comparison with the results from light microscopy. Cuspidothrix strains found in Bulgarian waterbodies showed high genetic similarity to those isolated and sequenced from Asia (Japan, China) and Northern Europe (Norway, Finland).

Effect of reservoir size on water quality in coastal reservoirs during desalinization period using numerical model

Abstract Coastal reservoirs are water storage structures constructed near the river estuary to supply water to coastal areas. One of the most important aspects related to performance of these structures is the effect of reservoir size on the flow and water quality. For this purpose, MIKE3, a 3D numerical software was used in the present work. The case study included proposed a coastal reservoir located on the coastlines of the Caspian Sea in the vicinity of Tajan River estuary. To conduct this research, four types of reservoirs with different sizes were considered. Input parameters to the model included 5-year flood of Tajan River, initial reservoir salinity and ambient temperature data. The results showed that construction of a shallower reservoir due to better surface and depth mixing could achieve higher water salinity during the desalinization period. Furthermore, the greatest water temperature change value was determined after passing hydrograph peak discharge, which shows the effect of inflow on reservoir water quality. Finally, the results of water density revealed that the decreasing trend of water density occurred mostly due to the decreasing water salinity in the reservoir.

Видовий склад водоростей солоних приморських водойм Приазовського національного природного парку

The paper is devoted to the researches of species composition and taxonomic structure of algae in the saline coastal reservoirs of the Pryazov National Natural Park (PNNP). It is established that species composition of algae in the studied reservoirs under modern conditions includes 153 species. These species represented 7 divisions, 11 classes, 32 orders, 61 families, 92 genera. The highest species richness at the level of divisions showed Cyanoprokaryota (43.8% of the total number of species), Bacillariophyta (32.0%) and Chlorophyta (20.9%). These divisions include 148 species and form the basis of the species composition in the studied water bodies. The leading orders of algae in the researched reservoirs were Oscillatoriales and Synechococcales (23 and 20 species respectively). The most diversely represented families were: Oscillatoriaceae (13 species), Nostocaceae, Leptolyngbyaceae, Naviculaceae (8 each), Microcoleaceae, Bacillariaceae (7 each). The top list of the genera by this parameter: Leptolyngbya (6 species), Lyngbya, Nostoc, Phormidium, Nitzschia (5 each), Calothrix, Kamptonema, Cocconeis, Navicula (4each).The highest frequency of occurrence among the identified species had also diatoms, cyanoprokaryotes and green algae: Halamphora coffeiformis (5.26%), Lyngbya aestuarii (4.21%), Cladophora siwaschensis (3.51%), Hantzschia amphioxys (3.33%), Nodularia harveyana (2.98%).Our researches demonstrate that species composition of algae of the studied saline coastal reservoirs of PNNP is quite impoverished in comparison with the partial soil algae flora, as well as the species list of algae of the freshwater reservoirs and seas of Ukraine. Specific features of the taxonomic composition of the saline coastal reservoirs are manifested in the association of organisms of fresh, marine and terrestrial habitats.

A coastal reservoir for Greater Sydney water supply in Shoalhaven river – a preliminary study

Abstract Australia is the driest inhabited continent on earth, and most of its population is concentrated along the coastal line. In recent years, extreme climate events such as floods and droughts have occurred more frequently. Sydney, as the largest city in Australia, requires a reliable water supply. Many solutions have been conducted to secure its water supply. This paper is focused on future water supply for the Greater Sydney area. The analysis supports the concept that in runoff-rich regions like Greater Sydney, there is no water shortage but a lack of water storage. The novel technology, coastal reservoirs, can increase the storage capacity of freshwater in the sea. The average annual discharge at Shoalhaven River mouth is estimated as 1,334 gigalitres. By comparison, the average annual inflow to the Warragamba Dam, which supplies 80% of Sydney's drinking water, is 1,069 gigalitres. This paper discusses how to apply a Coastal Reservoir at the Shoalhaven River mouth to secure additional water supply for ever-growing Greater Sydney. The proposed reservoir with a capacity of 500 gigalitres could supply 1,000 gigalitres of water per year with a reliability of 90%. A preliminary design of the reservoir is demonstrated.

Species Structure of Algae of the Saline Coastal Reservoirs of the Pryazov National Natural Park, Ukraine

Species Structure of Algae of the Saline Coastal Reservoirs of the Pryazov National Natural Park, Ukraine

Spatio-temporal variations of salinity and analysis of desalination factors in a Chinese coastal storage reservoir

Coastal reservoirs could be used to store freshwater in coastal cities, but the conversion of coastal reservoirs to freshwater reservoirs is relatively time-consuming, and coastal reservoirs are facing a risk of salinization. Taking Zhuyu Lake as the research object, the Spatio-temporal variations of water salinity under different seasons were investigated using the field survey and modeling. The influencing factors of the water salinity of the reservoir were analyzed to discover the variation mechanism. The results showed that the disturbance of overlying water is the most significant factor affecting the salt release of sediment, and salt release was increased by 63.3% with the disturbance. The depth of the overlying water and the salt content of bottom sediment also significantly affected the release of salt, with maximum enhancement by 23.1% and 45.6%, respectively. The microbial content in the bottom mud played an essential role in maintaining the salt, and inhibiting the microbial activity could enhance the release of salt by 35.7%. Therefore, disturbing the sediment by using disturbance ships or aeration devices, and the establishment of a long-term periodic plant harvesting belt could be used in the coastal fresh reservoirs desalination and slowing down the salinization of fresh reservoirs.

Environmental drivers of nitrous oxide emission factor for a coastal reservoir and its catchment areas in southeastern China

While Asia is projected to be one of the major nitrous oxide (N2O) sources in the coming decades, a more accurate assessment of N2O budget has been hampered by low data resolution and poorly constrained emission factor (EF). Since urbanized coastal reservoirs receive high nitrogen loads from diverse sources across a heterogeneous landscape, the use of a single fixed EF may lead to large errors in N2O assessment. In this study, we conducted high spatial resolution sampling of dissolved N2O, nitrate-nitrogen (NO3−–N) and other physico-chemical properties of surface water in Wenwusha Reservoir and other types of water bodies (river, drainage channels, and aquaculture ponds) in its catchment areas in southeastern China between November 2018 and June 2019. The empirically derived EF (calculated as N2O–N:NO3−-N) for the reservoir showed considerable spatial variations, with a 10-fold difference ranging from 0.8 × 10−3 to 8.8 × 10−3. The average EF varied significantly among the four types of water bodies in the following descending order: aquaculture ponds > river > drainage channels > reservoir. Across all the water bodies, the mean EF in summer was 1.8–3.5 and 1.7–2.8 fold higher than that in autumn and spring, respectively, owing to the elevated water temperature. Overall, our derived EF deviated considerably from the IPCC default value, which implied that the use of default EF could result in over- or under-estimation of N2O emissions by up to 42%. We developed a multiple regression model that could explain 82% of the variance in EF based on water temperature and the ratio between dissolved organic carbon and nitrate-nitrogen (p < 0.001), which could be used to improve the estimate of EF for assessing N2O emission from coastal reservoirs and other similar environments.

Hydraulic Treatise of Untreated Water Reservoir Design of Indonesia's National Capital Integrated Coastal Development Offshore Dike

Wurjanto, A. and Mukhti, J.A., 2021. Hydraulic treatise of untreated water reservoir design of Indonesia's national capital integrated coastal development offshore dike. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 166–170. Coconut Creek (Florida), ISSN 0749-0208. Coastal flooding and land subsidence are among the main issues for cities along the northern coast of Java Island. The Indonesian government planned to build integrated coastal protection along the northern coast. For the Capital City of Jakarta, the offshore dike will be complemented with a coastal reservoir to store freshwater for municipal uses. To overcome the occasional extreme weather, an untreated water reservoir (UWR) is required. This paper discussed the design of UWR pumping capacity and flood gate design of capital offshore dike through a hydrodynamic analysis with Delft3D. Flood hydrographs of extreme rainfall were created based on the data provided by the Ministry of National Planning. Bathymetry and tidal source were collected from GEBCO and NAOTide respectively. Hydrodynamic modeling was performed with variations on pump capacity and river input flows. The hydrodynamic model shows that the current UWR design can hold up to a 10-year flood without pumping. For more extreme floods, the UWR can also retain the water below the high water level with the help of pumps. The water elevation can be back to normal at -5.0 mLWS within a day of pumping with 1,600 m3/s.

Inclusion of slow infiltration in determining the influence time of saline sediments on reservoir water

The influence time of polluted sediments on water quality, as well as the influence degree, plays a key role in decision-making for sediment pollution control. However, factors that determine influence time, especially slow infiltration through sediments, are poorly known. Further, there is a lack of corresponding indexes and efficient models to accurately identify the critical moment in determining the influence time from the dynamic process of interaction between downward advection (infiltration) and upward diffusion at the sediment-water interface. Therefore, this article focuses on methods for determining the influence time of saline sediments on reservoir water salinisation. An alternative expression of Péclet number (Pe=uCD∂C/∂xx=0) is proposed to characterise the transient relative role of downward advection versus upward diffusion on the transport of non-reactive solutes; Pe = 1 can be used as an exact criterion for identifying the critical moment when saline sediments no longer affect the overlying water. We then developed a single-domain model that does not require an alternate run the two subdomains in solving processes, enabling to flexibly simulate sediment-water interactions, both effectively and efficiently. By combining this model with the alternative Pe, the influence time of saline sediments on reservoir water can be accurately determined. We used the planned Muguandao Coastal Reservoir, Qingdao, China, as an example to explore the effects of infiltration on the influence time. The influence time shortens with infiltration rates in a power function relationship and decreases from 970 years to 19.3 years in the rate range of (1–7) ×10−2 m/year. Furthermore, based on the simulation and sensitivity analysis, we suggest a simple formula (t=5.25D/u2) to directly predict the influence time of saline sediments on water salinisation for shallow mixed coastal reservoirs. The importance of understanding slow infiltration in determining the influence time is discussed.

Eutrophication increases deterministic processes and heterogeneity of co-occurrence networks of bacterioplankton metacommunity assembly at a regional scale in tropical coastal reservoirs

Understanding microbial metacommunity assembly and the underlying methanisms are fundamental objectives of aquatic ecology. However, little is known about how eutrophication, the primary water quality issue of aquatic ecosystems, regulates bacterioplankton metacommunity assembly at a regional scale in reservoirs. In this study, we applied a metacommunity framework to study bacterioplankton communities in 210 samples collected from 42 tropical coastal reservoirs in the wet summer season. We found that the spatial pattern of bacterioplankton community compositions (BCCs) at a regional scale was shaped mainly by species sorting. The reservoir trophic state index (TSI) was the key determinant of bacterioplankton metacommunity assembly. BCC turnover increased significantly with the TSI differences between sites (∆TSI) when ∆TSI was < 20, but remained at a level of about 80% when ∆TSI was > 20. Compared to oligo-mesotrophic and mesotrophic reservoirs, increased heterogeneity of co-occurrence bacterioplankton networks and bacterioplankton β-diversity were observed across eutrophic reservoirs. We propose that larger variation in phytoplankton community assembly may play directly or indirectly deterministic processes in controlling the bacterioplankton metacommunity assembly and became the potential mechanisms behind the observed higher BCC heterogeneity across the eutrophic reservoirs. Our research contributes to a broader understanding of the ecological effects of eutrophication on reservoir ecosystems and provides clues to the management of the tropical coastal reservoirs.

Combined effect of inland groundwater input and tides on flow and salinization in the coastal reservoir and adjacent aquifer

Coastal reservoirs can alleviate the shortage of freshwater in the nearshore zone. Inland groundwater and tides can cause hydraulic gradients between seawater and reservoir water and affect the salt concentration of coastal reservoirs; however, the mechanism is poorly understood. Laboratory experiments and numerical simulations were conducted to investigate the combined effect of inland groundwater inputs and tides on the surface/subsurface flow and salinization dynamics of the coastal reservoir and adjacent aquifer. The results indicated that inland groundwater followed two pathways before discharging into the sea, regardless of the tidal conditions. The predominant pathway led inland groundwater to be discharged to the coastal reservoir and then to sea. The other pathway encompassed the entire aquifer underlying the reservoir bed and terminated at the aquifer–sea interface. As the inland groundwater input increased, the groundwater entering the reservoir also increased, whereas the ratio of the fresh groundwater transported through the reservoir to the total groundwater input decreased. Tidal pumping allowed more seawater to intrude into the coastal reservoir and adjacent aquifer compared with nontidal conditions. This caused a larger proportion of groundwater to be discharged to the coastal reservoir, with the density-driven flow and water/salt exchange across the aquifer-reservoir interface also enhanced. As the inland groundwater input increased, salinization of the coastal reservoir decreased and the inhibition of the inland groundwater input on salinization also decreased. This study contributes to the improved management of such coastal infrastructures.