Effects Of Freshwater Discharge Research Articles

Effect of Freshwater Discharge on the Water Quality in Cheonsu Bay, West Coast of Korea

Effect of Freshwater Discharge on the Water Quality in Cheonsu Bay, West Coast of Korea

Effect of Freshwater Discharge From Estuary Dam on Residual Circulation in Bifurcated Channel

AbstractThe residual structure of the inner part of the Yeongsan River estuary has been reported to be a multi‐layer vertical structure, unlike the two‐layer vertical structure of a typical estuary, due to irregular freshwater discharge. The inner estuary has a main channel connected to the open sea, and a bifurcated channel system (sub‐channel) in its central part, which can affect the residual current. In this study, field observations of three‐dimensional velocity and salinity were conducted to understand the discharge effects on the residual current at bifurcated channels. The residual flows were estimated using least‐squares harmonic analysis. The relative contributions of advection acceleration and friction terms to nonlinear effects were evaluated using along‐channel momentum balance. In the absence of freshwater discharge, the flow patterns were dominated by tidal dynamics in the sub‐channel rather than the main channel, whereas most flow patterns during freshwater discharge were dominated by near‐surface strong velocity in the main channel. A multi‐layer vertical residual structure was observed during the non‐discharge period in the main channel, which was caused by the insertion of upstream residual flow from the sub‐channel. Nonlinear effects occurred at the bifurcation point of the two channels. During the non‐discharge period, the advection term was most dominant, whereas the vertical friction term was dominant during the discharge period. Moreover, the magnitude of the horizontal friction term was larger than that of the advection term. Therefore, freshwater discharge can lead to an increase in the friction term, which in turn can markedly affect the residual circulation.

Effect of Freshwater Discharge from a Water Reservoir on the Flow Circulation in the Semi-Closed Harbor

담수 ìœ ìž ì´ 항만 내 해수순환에 미치는 영향을 조사하기 위하여, 인천 남항의 남측에 위치한 ì‹ êµ­ì œ 여객터미널 해역에 3차원 ìœ ë™ 수치 모델을 구축 및 ì ìš©í•˜ì˜€ë‹¤. 수치 모델의 모의 기간은 경기만 지역의 평수기인 5월 15일부터 6월 30일까지 약 45일이며, 모델 결과와 관측자료의 비교를 통하여 ìœ ë™ê³¼ 염분 변화에 관한 모델의 재현성을 검증하였다. ì‹ êµ­ì œ 여객터미널에 영향을 미치는 담수 공급원은 한강과 항만 동쪽에 위치한 용현 갯골 ìœ ìˆ˜ì§€ê°€ 있다. ìœ ìˆ˜ì§€ì˜ ìœ ë¬´ì— 따른 잔차류 결과를 분석해 ë³´ë©´, 한강과 ìœ ìˆ˜ì§€ê°€ 모두 ê³ ë ¤ëœ 실험안이 한강만을 ê³ ë ¤í•œ 실험안보다 염분 경사에 의한 2층 흐름 구조(표층은 외해 방향, ì €ì¸µì€ 항 내를 향한 흐름 구조)가 ìˆ˜í‰ì ìœ¼ë¡œ 더 강하게 발달한다. 이는, 한강으로부터의 담수 영향보다 ìœ ìˆ˜ì§€ë¡œë¶€í„°ì˜ 담수 영향이 ì‹ êµ­ì œ 여객터미널 해역에서 더 크다는 것을 시사한다. 또한, 잔차류의 2층 흐름 구조는 북쪽에 위치한 인천 남항보다, 남쪽에 위치한 ì‹ êµ­ì œ 여객터미널에서 더 강한 2층 흐름 구조가 발생한다. 이 프로세스는 ìœ ìˆ˜ì§€ë¡œë¶€í„°ì˜ 담수와 항 내로 ì „íŒŒëœ 조류가 만나 ì‹ êµ­ì œ 여객터미널 방향으로 íšŒì „ë˜ì–´ ì „íŒŒë˜ë©´ì„œ, 남쪽에 위치한 ì‹ êµ­ì œ 여객터미널에 ì €ì—¼ìˆ˜ê°€ ì „ë‹¬ë¨ì— 따라 형성된다. 이러한 흐름은 ì‹ êµ­ì œ 여객터미널 ì „ë©´ë¶€ì—ì„œ ìˆ˜í‰ì ì¸ 염분 경사에 의한 성층을 강화시키며, 강화된 성층은 2층 흐름 구조를 형성 및 ìœ ì§€ì‹œí‚¨ë‹¤. 따라서, 항만 내의 경압 작용에 의한 해수순환과 물질이동을 ìž¬í˜„í•˜ê³ ìž í• ë•Œ, ìœ ìˆ˜ì§€ì™€ 같은 êµ­ì§€ì ì¸ 담수 ìœ ìž ì›ì´ë¼ë„, 항만 내의 해수순환에 ì§€ë°°ì ì¸ 영향을 미치므로, 현장 관측 자료를 기반으로 ìœ ìˆ˜ì§€ì—ì„œ 방류되는 실시간 담수 ìœ ëŸ‰ì— 따른 수치모델을 수행해야 한다. 핵심용어: 담수 방류, 한강, ìœ ìˆ˜ì§€, 잔차 순환

Radium isotope ratios as a tool to characterise nutrient dynamics in a variably stratified temperate fjord

The effect of freshwater discharge on solute vertical mixing and horizontal transfer rates is evaluated in a variably stratified temperate fjord (Killary Harbour, Ireland) using the activity ratios of 224Ra and 223Ra in the water column. With high river discharge (>1.7 × 106 m3 d−1), surface 224Ra/223Ra activity ratios (ARs) decreased from 18.0 ± 7.1 to 8.6 ± 0.9 from the inner to the outer fjord and the system becomes stratified, resulting in clear differences of 224Ra/223Ra ARs between surface and bottom layers. When river discharge was low (<0.6 × 106 m3 d−1), 224Ra/223Ra ARs dipped from 19.6 ± 5.1 to 8.0 ± 1.8 in the inner system before increasing again towards the outlet to the sea up to 11.3 ± 3.6, and the water column was well mixed: the difference in 224Ra/223Ra ARs and salinity between surface and bottom layers was minimal. Longitudinal seaward decreases of surface water 224Ra/223Ra ARs within the inner fjord independently of river discharge suggested that the contribution of benthic-pelagic coupling to surface solute inventories is small in the inner section of the system. Conversely, the increase of 224Ra/223Ra ARs during low discharge conditions indicated that the slower flushing of the system, coupled with a well-mixed water column, facilitated solute transfers from deeper waters to the surface in the outer fjord. The effect of discharge on the residence time of water in the inner fjord was also determined using radium ages: longitudinal water flushing timescales are quickly reduced in the inner part of the bay with increasing discharge. We show that the degree of vertical mixing is an important driver of nutrient ratios in the system. Retention of soluble reactive phosphorus (SRP) and Ra in deep water and a higher molar N:P ratio in surface water were more likely under stratified conditions. Stratification may therefore amplify the effect of variable watershed inputs on the estuarine N:P ratio in Killary Harbour.

Effect of freshwater discharge from Namgang Dam on ichthyoplankton assemblage structure in Jinju Bay, Korea

The movement of fish eggs and larvae in bay and estuarine systems is affected by freshwater discharge. In this study, the assemblage structures of ichthyoplankton eggs and larvae were assessed for the first time in Jinju Bay, South Korea, to identify the spawning and nursery functions of the bay. Fish eggs and larvae and several environmental parameters were sampled monthly from April 2015 to March 2016 inside and outside of the bay. Within the bay we collected eggs and larvae from 25 and 35 species, respectively, indicating greater diversity than outside the bay, where we collected eggs and larvae of 20 and 28 species, respectively. Fluctuations in water temperature and salinity were larger inside than outside of the bay, and chlorophyll-a concentration was higher within the bay, likely due to discharge from the Namgang Dam, which causes water to flow from the inside to the outside of the bay. This process influences fish larva abundance, such that more larvae are found outside than inside the bay. We also found that 28 fish species use Jinju Bay as a spawning ground. For some species, the timing of egg and larva appearance differed inside and outside of the bay, suggesting that the timing of spawning may differ between the two environments.

Effect of Freshwater Discharge on the Nakdong River Estuary: Mooring Observations of Water Temperature and Salinity

Effect of Freshwater Discharge on the Nakdong River Estuary: Mooring Observations of Water Temperature and Salinity

Abrupt mortality of marine invertebrates at the Younger Dryas-Holocene transition in a shallow inlet of the Goldthwait Sea

The late Pleistocene–early Holocene transition period was characterized by rapid environmental change. Here, we investigate the impact of these changes on the marine invertebrates living in a shallow inlet of the post-glacial Goldthwait Sea. The site is located near Baie-Comeau (QC, Canada), where a number of remarkably well-preserved shell deposits are found along the Rivière aux Anglais Valley on the north shore of the St. Lawrence maritime estuary. Seven phyla of marine invertebrates with a minimum of 25 species or taxa were inventoried in a shell deposit, dominated by a community of Hiatella arctica with Mytilus edulis and barnacles composing the subcommunity. The majority of taxa identified in the shell deposit are boreal and sub-Arctic species; however, temperate species that exist today in the St. Lawrence maritime estuary have not been found. Based on marine invertebrate diversity and δ18O(CaCO3) of Mytilus edulis, the water in the shallow inlet of the Goldthwait Sea must have been cold and saline. The range of AMS 14C ages from 15 Mytilus edulis, constrained to 10,900 and 10,690 cal. yr BP, and exceptional state of preservation of adult and juvenile molluscan specimens suggest the abrupt mortality of entire invertebrate communities due to changing hydrodynamic conditions that included the combined effect of freshwater discharge from the receding Laurentide Ice Sheet and rapid isostatic uplift.

The impact of environmental factors on marine turtle stranding rates.

Globally, tropical and subtropical regions have experienced an increased frequency and intensity in extreme weather events, ranging from severe drought to protracted rain depressions and cyclones, these coincided with an increased number of marine turtles subsequently reported stranded. This study investigated the relationship between environmental variables and marine turtle stranding. The environmental variables examined in this study, in descending order of importance, were freshwater discharge, monthly mean maximum and minimum air temperatures, monthly average daily diurnal air temperature difference and rainfall for the latitudinal hotspots (-27°, -25°, -23°, -19°) along the Queensland coast as well as for major embayments within these blocks. This study found that marine turtle strandings can be linked to these environmental variables at different lag times (3–12 months), and that cumulative (months added together for maximum lag) and non-cumulative (single month only) effects cause different responses. Different latitudes also showed different responses of marine turtle strandings, both in response direction and timing.Cumulative effects of freshwater discharge in all latitudes resulted in increased strandings 10–12 months later. For latitudes -27°, -25° and -23° non-cumulative effects for discharge resulted in increased strandings 7–12 months later. Latitude -19° had different results for the non-cumulative bay with strandings reported earlier (3–6 months). Monthly mean maximum and minimum air temperatures, monthly average daily diurnal air temperature difference and rainfall had varying results for each examined latitude. This study will allow first responders and resource managers to be better equipped to deal with increased marine turtle stranding rates following extreme weather events.

Conditions for tidal bore formation in convergent alluvial estuaries

Over the last decade there has been an increasing interest in tidal bore dynamics. However most studies have been focused on small-scale bore processes. The present paper describes the first quantitative study, at the estuary scale, of the conditions for tidal bore formation in convergent alluvial estuaries. When freshwater discharge and large-scale spatial variations of the estuary water depth can be neglected, tide propagation in such estuaries is controlled by three main dimensionless parameters: the nonlinearity parameter ε0, the convergence ratio δ0 and the friction parameter ϕ0. In this paper we explore this dimensionless parameter space, in terms of tidal bore occurrence, from a database of 21 estuaries (8 tidal-bore estuaries and 13 non tidal-bore estuaries). The field data point out that tidal bores occur for convergence ratios close to the critical convergence δc. A new proposed definition of the friction parameter highlights a clear separation on the parameter plane (ϕ0,ε0) between tidal-bore estuaries and non tidal-bore estuaries. More specifically, we have established that tidal bores occur in convergent estuaries when the nonlinearity parameter is greater than a critical value, εc, which is an increasing function of the friction parameter ϕ0. This result has been confirmed by numerical simulations of the two-dimensional Saint Venant equations. The real-estuary observations and the numerical simulations also show that, contrary to what is generally assumed, tide amplification is not a necessary condition for tidal bore formation. The effect of freshwater discharge on tidal bore occurrence has been analyzed from the database acquired during three long-term campaigns carried out on the Gironde/Garonne estuary. We have shown that in the upper estuary the tidal bore intensity is mainly governed by the local dimensionless tide amplitude ε. The bore intensity is an increasing function of ε and this relationship does not depend on freshwater discharge. However, freshwater discharge damps the tidal wave during its propagation and thus reduces ε and consequently limits the tidal bore development in the estuary. To take into account this process in the tidal-bore scaling analysis, it is necessary to introduce a fourth external parameter, the dimensionless river discharge Q0.

Seasonal changes in the subtidal benthic macrofauna of a mangrove coast in northern Brazil

Melo, K.R., Tagliaro, C.H. and, Beasley, C.R., 2013.Seasonal changes in the subtidal benthic macrofauna of a mangrove coastMangrove coasts in northern Brazil are subject to seasonal discharges of freshwater input from rivers and terrestrial runoff. However, little is known about the effects of freshwater discharge on the subtidal benthos in the region. Thus, three sites, each representing a different level of seasonal discharge, Canela island (low), Ajuruteua beach (medium), and the Caeté Bay (high) were sampled in the dry (October) and wet (April/May) seasons of 2007 and 2008, respectively. Sampling was carried out using a Petersen grab and a bottom dredge (total n=74). Additional replicas (n=12) were obtained by grab for sediment analyses. Salinity and turbidity of the bottom waters, and percentage of silt/clay in the sediment were also measured. Benthic macrofauna and environmental data were analyzed using uni- and multivariate techniques. A total of 661 individuals were distributed among 47 taxa of which polychaetes and crustaceans dominated at all three sites. No significant differences in macrofaunal abundance were found among sites and dates. At all sites, in the wet season, the number of taxa was low and dominance was high, especially in the Caeté Bay. The polychaete Nephtys fluviatilis only occurred in the Caeté Bay in the wet season, and yet was the dominant taxon (22.7% of total abundance). The Ajuruteua beach and Canela island samples were composed of typically marine taxa. The polychaete Armandia sp., the gastropod Olivella minuta, mysiid and phoxocephalid crustaceans and the echinoderm family Mellitidae were most abundant in the dry season at Canela island. Salinity was the most important environmental factor associated with high numbers of taxa in the dry season. Silt and turbidity were associated with low numbers of taxa in the wet season. In conclusion, the subtidal benthic macrofauna at Canela island, Ajuruteua beach and the Caeté Bay is mainly composed of polychaetes and crustaceans. The higher freshwater discharge in the wet season, resulting in lower salinity, higher percentage silt and greater turbidity, is associated with lower abundance, fewer taxa and a different faunal composition at Canela and Ajuruteua, and strong dominance of an oligohaline polychaete in the Caeté Bay

Using Ecopath with Ecosim to Explore Nekton Community Response to Freshwater Diversion into a Louisiana Estuary

AbstractCurrent methods to restore Louisiana's estuaries include the reintroduction of Mississippi River water through freshwater diversions to wetlands that are hydrologically isolated from the main channel. The reduced salinities associated with freshwater input are likely affecting estuarine nekton, but these effects are poorly described. Ecopath with Ecosim was used to simulate the effects of salinity changes caused by the Caernarvon freshwater diversion on species biomass distributions of estuarine nekton. A base model was first created in Ecopath from 5 years of monitoring data collected prior to the opening of the diversion (1986–1990). The effects of freshwater discharge on food web dynamics and community composition were simulated using a novel application of Ecosim that allows the input of salinity as a forcing function coupled with user‐specified salinity tolerance ranges for each biomass pool. The salinity function in Ecosim not only reveals the direct effects of salinity (i.e., increases in species biomass at their optimum salinity and decreases outside the optimal range) but also the indirect effects resulting from trophic interactions. Through multivariate analyses we determined that the simulated species biomass distributions in the estuary change significantly with distance from the diversion. However, the simulations do not show a significant difference estuarywide between the modeled distributions (with pooling of the data from different distances) before and after the opening of the diversion. This indicates a redistribution of species in the estuary rather than the replacement of species within the estuarine nekton community. The salinity function is a useful addition to the Ecopath with Ecosim software for estuarine ecologists and fisheries managers.Received January 31, 2011; Acceptdate November 30, 2011

Effect of the Mahanadi River on the Development of Storm Surge Along the Orissa Coast of India: A Numerical Study

River-ocean coupled models are described for the evaluation of the interaction between river discharge and surge development along the Orissa coast of India. The models are used to study the effect of fresh water discharge from the Mahanadi River on the surge response along the Orissa coast due to the October 1999 super cyclone which led to severe flooding of the coastal and delta regions of Orissa. The so-called 1999 Paradip cyclone was one of the most severe cyclones; causing extensive damage to property and loss of lives. The present study emphasizes the impact of the Mahanadi River on overall surge development along the Orissa coast. Therefore, we have developed a location specific fine resolution model for the Orissa coast and coupled it with a one–dimensional river model. The numerical experiments are carried out, both with and without inclusion of fresh water discharge from the river. The bathymetry for the model has been taken from the naval hydrographic charts extending from the south of Orissa to the south of west Bengal. A simple drying scheme has also been included in the model in order to avoid the exposure of land near the coast due to strong negative sea-surface elevations. The simulations with river-ocean coupled models show that the discharge of fresh water carried by the river may modify the surge height in the Bay, especially in the western Bay of Bengal where one of the largest river systems of the east coast of India, the Mahanadi River, joins with the Bay of Bengal. Another dynamic effect of this inlet is the potentially deep inland penetration of the surge originating in the Bay. The model results are in good agreement with the available observations/estimates.

Analytical Model of Salt Budget in the Upper Indian River Lagoon, Florida USA

Effect of freshwater discharge on the long-term salt balance in the Northern and Central Indian River Lagoon (IRL) is successfully simulated by a new analytical solution to a water balance-based one-dimensional salt conservation equation. Sensitivity tests show that the salinity levels drop abruptly even during the dry season (November to May) due to the high surface runoff discharge caused by tropical storms, depressions, and passage of cold fronts. Increasing surface runoff and direct precipitation has risen by ten times, lowering the salinity level down to 12psu in the Northern Central zone, and to 17 psu in the Northern zone. However, the salinity level in the Southern Central zone has decreased to 25 psu. High sensitivity of the Northern Central zone to freshwater discharge can be partially explained by a rapid urbanization in this zone. During the dry season, less sensitivity of the Southern Central zone to the increased surface runoff is attributed to the proximity of the zone to the Sebastian Inlet and a strong diffusion condition possibly resulting from the seawater intrusion to the surficial aquifer at the Vero Beach. During the wet season, however, the whole study area is highly sensitive to freshwater discharge due to the weak diffusion conditions. High sensitivity of the IRL to the given diffusion conditions guarantees that the fresh-water release occurs during strong wind conditions, achieving both flood control in the drainage basin and a proper salinity regime in the IRL.

Effects of Freshwater Discharge in Sandy Beach Populations: The Mole Crab Emerita brasiliensis in Uruguay

Sandy beaches are ecosystems which are heavily affected by human activities. An example of this is freshwater discharges, which are known to change salinity, temperature and nutrient regimes and degrade nearshore environments. However, the effects of this kind of disturbance on sandy beach fauna have been little studied. This paper reports the spatial effects of a man-made freshwater canal discharge on the population structure, abundance and reproductive characteristics of the sandy beach mole crab Emerita brasiliensis. Along the 22km of sandy beach sampled, the mole crab showed a marked longshore variability in population structure and abundance. Abundance of different population components (juveniles, males, females and ovigerous females) significantly decreased towards the canal. Population structure by sex and size, individual weight, fecundity and female maturity patterns at size also displayed a non-linear response to the distance from the freshwater discharge. Only the size structure of males did not follow this pattern. For males, spatial heterogeneity enhanced the detection of density-dependence at less disturbed sites. The authors conclude that artificial freshwater discharges could significantly influence the distribution, abundance and life-history traits of the biota of sandy beaches, and that further study of these ecosystems should include human activities as important factors affecting spatial and temporal trends. The need to consider different spatial and temporal scales in order to detect the effect of anthropogenically-driven impacts in sandy beach populations is stressed.

Numerical Simulation of Currents and Density in a Bay Considering Variable Conditions of Outer Ocean

When the phenomena in a bay are calculated, the open boundary is often located around the mouth of the bay. On the other hand, the effect of physical conditions of outer ocean is essential for such phenomena as thermohaline front or intrusion of warm water mass into the bay. However, it is difficult to elucidate the mechanism of such phenomena if the constant conditions are applied for the open boundary. In the present study, the influences of outer ocean state on the phenomena in the bay were investigated by numerical simulations. At first, the effects of fresh water discharge, surface cooling and outer ocean condition on the structure of thermohaline front was examined for an idealized model basin. Next, the numerical simulations were carried out for Tokyo Bay and the influence of water temperature distribution of Sagami bay was discussed. In the calculation considering the effects of outer bay region, the satellite remote sensing data was used for determining the sea surface temperature.

Effect of freshwater discharge, intrusions of coastal water, and bathymetry on zooplankton distribution in a Norwegian fjord system

Effect of freshwater discharge, intrusions of coastal water, and bathymetry on zooplankton distribution in a Norwegian fjord system

The Effect of Freshwater Discharge from the Godavari River on the Occurrence of Local Upwelling off the East Coast of India

A numerical model is described and applied to investigate the combination of the wind- and estuarially-driven circulation of water off the east coast of India. A previous numerical modelling study has shown that the estuarial discharge from the Hugli and Mahanadi Rivers may, consistently with an interpretation of observational data, inhibit the occurrence of coastal upwelling as far south as Visakhapatnam. Further south of this location, there is a substantial discharge of freshwater during the monsoon season into the Bay of Bengal from the Godavari River that might possibly have a similar suppressive effect on the coastal upwelling dynamics. In a process-orientated evaluation, it is shown that a representative rate of discharge from the Godavari River leads to a marked cross-shelf spread of a plume of relatively low-salinity water and that the associated dynamical structure is then correspondingly modified so as to weaken the local coastal upwelling tendencies in the surface layers of the ocean that would exist in the sole presence of south-westerly wind-stress forcing and the northern estuarial outflow.