Effects Of Freshwater Input Research Articles

A Song of Wind and Ice: Increased Frequency of Marine Cold‐Spells in Southwestern Patagonia and Their Possible Effects on Giant Kelp Forests

AbstractIn contrast to other coastal regions of the world, the giant kelp (Macrocystis pyrifera) ecosystem in southwestern Patagonia has been persistent in area and associated biodiversity in the last decades. In this ecoregion, sea surface temperature (SST) records have consistently remained below the upper thermal threshold for kelp survival, however, no studies have analyzed the spatiotemporal variability of SSTs and their anomalies across the geographical diversity of the southwestern Patagonian coastline. We explored the geographical distribution of extreme warm and cold events in this region from latitudes 47°–56°S in a range of ∼1,000 km, identifying the dates and spatial distribution of marine heatwaves (MHWs) and marine cold‐spells (MCSs) from 1982 to 2020. Results show that a peak in the number of MHWs occurred in the great El Niño year of 1998. Additionally, the 2014–2019 period has had more severe and extreme MCSs than the previous decades. We discuss the origin of these events with a focus on three main processes: (a) geographically constrained cold events caused by glacier melting, (b) regional cold events caused by extreme winds linked to the position of the polar front, and (c) extensive SST anomalies linked to planetary‐scale events such as El Niño and La Niña. Overall, those processes were conductive to counteract global warming trends locally/regionally, highlighting southwestern Patagonia as a possible climatic refugium for the giant kelp ecosystem. Despite this, the effects of freshwater inputs and storm turbulence on the exposed coasts facing the Southern Ocean may cause new kinds of stress on this ecosystem.

Global temperature calibration of the Long chain Diol Index in marine surface sediments

The Long chain Diol Index (LDI) is a relatively new organic geochemical proxy for sea surface temperature (SST), based on the abundance of the C30 1,15-diol relative to the summed abundance of the C28 1,13-, C30 1,13- and C30 1,15-diols. Here we substantially extend and re-evaluate the initial core top calibration by combining the original dataset with 172 data points derived from previously published studies and 262 newly generated data points. In total, we considered 595 globally distributed surface sediments with an enhanced geographical coverage compared to the original calibration. The relationship with SST is similar to that of the original calibration but with considerably increased scatter. The effects of freshwater input (e.g., river runoff) and long-chain diol contribution from Proboscia diatoms on the LDI were evaluated. Exclusion of core-tops deposited at a salinity < 32 ppt, as well as core-tops with high Proboscia-derived C28 1,12-diol abundance, resulted in a substantial improvement of the relationship between LDI and annual mean SST. This implies that the LDI cannot be directly applied in regions with a strong freshwater influence or high C28 1,12-diol abundance, limiting the applicability of the LDI. The final LDI calibration (LDI = 0.0325 × SST + 0.1082; R2 = 0.88; n = 514) is not statistically different from the original calibration of Rampen et al. (2012) (https://doi.org/10.1016/j.gca.2012.01.024), although with a larger calibration error of 3 °C. This larger calibration error results from several regions where the LDI does not seem to have a strong temperature dependence with annual mean SST, posing a limitation on the application of the LDI.

Effects of freshwater inputs on soil quality in the Yellow River Delta, China

With the degradation or loss of coastal wetlands, more and more restoration projects have been widely conducted. Freshwater inputs have been proved to be an effective restoration way for degraded coastal wetlands. However, little information is available on the changes in soil quality caused by freshwater inputs. Soil samples were collected to a depth of 50 cm in freshwater restoration wetlands (FRW), tidal salt marshes with Suaeda salsa (SSM) and tidal salt marshes with Tamarix chinensis (TSM) in the Yellow River Delta, China, in August 2015, to investigate the changes in soil quality after freshwater inputs. Our results showed that soil salinity was significantly higher in natural wetlands than that in freshwater restoration wetlands (p < 0.05), while no significant differences in soil organic matter (SOM) were observed among three wetlands (p > 0.05). Cluster analysis and principal component analysis exhibited that soil samples in natural wetlands and freshwater restoration wetlands were clearly distinguished. Soil properties were screened and transformed to establish a soil quality index (SQI) for the assessment of soil quality. Soil salinity, SOM and silt were selected in the minimum data set in this study. Although there were no statistical differences in SQIs (p > 0.05), both linear SQI (SQIL) and non-linear SQI (SQINL) for three wetlands followed the order: SSM > FRW > TSM. And the SQIL values were lower compared with SQINL. The contributions of soil salinity to SQIL for three wetlands and SQINL for TSM and SSM were the highest in the minimum data for three wetlands, while SOM showed the highest contribution proportion of SQINL for FRW.

Absence of an effect of freshwater input on the stable isotope and fatty acid signatures of intertidal filter-feeders

Freshwater input is known to have the potential to influence marine pelagic and benthic communities through the export of nutrients, sediments and detritus. The increase in nutrients of riverine origin in coastal environments can enhance primary production in coastal areas, supporting a diverse and rich fauna. However, it is not clear how and to what extent these freshwater inputs influence marine populations. We investigated the potential effects of freshwater input on the diets of intertidal benthic organisms in situ on the east coast of South Africa, analysing their δ13C and δ15N stable isotope and fatty acid content. Specifically, we investigated the dietary regime of three barnacle and one mussel species in relation to their proximity to the mouths of large rivers. Strong dissimilarities among species were recorded with both techniques; however, no significant effect of freshwater input was observed for any of them. There are several possible explanations for these results, including rapid dilution, with fresh water near the river mouth being thoroughly mixed with seawater, resulting in a riverine influence being too weak to be detectable in the signatures of benthic populations. Our results contrast with a previous study conducted in the same area, where it was suggested that demersal organisms relied on freshwater-derived organic matter. Our study, however, showed no freshwater effect either within a few metres or tens of kilometres from the nearest large river mouths, supporting the notion that freshwater input does not play an important role for the benthic intertidal community in the ecosystems studied. Given that freshwater input is likely to diminish in the future, because of increased human abstraction of water, any potential effects of freshwater input on these marine populations are likely to be further reduced.

Effects of freshwater input and mariculture (bivalves and macroalgae) on spatial distribution of nanoflagellates in Sungo Bay, China

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 6:191-203 (2015) - DOI: https://doi.org/10.3354/aei00124 Effects of freshwater input and mariculture (bivalves and macroalgae) on spatial distribution of nanoflagellates in Sungo Bay, China Jiachang Lu1, Lingfeng Huang2,*, Yuanrong Luo2, Tian Xiao3, Zengjie Jiang4, Linnan Wu1 1College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, PR China 2Key Laboratory of the Ministry of Education for Coastal and Wetland Ecosystem, Xiamen University, Xiamen 361102, PR China 3Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, PR China 4Key Laboratory of Sustainable Development of Marine Fisheries, Ministry of Agriculture, Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao 266071, PR China *Corresponding author: huanglf@xmu.edu.cn ABSTRACT: Sungo Bay in northern China has been used for rearing bivalves and macroalgae for several decades. The bivalve culture areas (B-area) are located in the bay head, and the macroalgae culture areas (M-area) are located outside of the B-area. In field investigations, we compared the nanoflagellates (NF) in the B-area and the M-area during 4 seasons. After the field investigations, enclosure experiments were conducted during summer to study the effects of mariculture (bivalves and macroalgae) on NF. In the warm seasons (summer and autumn), during which there was an obvious freshwater input to the bay (especially during summer), NF abundance was negatively related to salinity and was higher in the B-area than in the M-area. In the enclosure experiments, an increase in NF abundance was observed after Day 4 in the bivalve enclosure, but not in the macroalgae enclosure. Considering that the B-area was the area of lower salinity, and the season of largest freshwater input was also the optimal growth season for bivalves, we suggest that the spatial distribution of NF in the warm seasons in Sungo Bay may be influenced by both freshwater input and mariculture. KEY WORDS: Nanoflagellates · Mariculture · Freshwater input · Sungo Bay Full text in pdf format PreviousCite this article as: Lu J, Huang L, Luo Y, Xiao T, Jiang Z, Wu L (2015) Effects of freshwater input and mariculture (bivalves and macroalgae) on spatial distribution of nanoflagellates in Sungo Bay, China. Aquacult Environ Interact 6:191-203. https://doi.org/10.3354/aei00124 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 6, No. 2. Online publication date: February 26, 2015 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2015 Inter-Research.

Aragonite undersaturation in Gwangyang Bay, South Korea: Effects of fresh water input

Dissolved inorganic carbon (DIC) and alkalinity were precisely measured for surface and bottom waters in Gwangyang Bay, Korea, during the four seasons to assess seasonal variations of aragonite saturation state (Ωarag). Both the surface and bottom waters were undersaturated with respect to aragonite during summer but were supersaturated during the other seasons. The summertime undersaturation of the surface waters with respect to aragonite may have been a result of the dilution effect caused by higher seasonal river runoff. In the bottom waters, the average DIC concentration increased by 40.6 μmol kg™1 from spring to summer, while the average alkalinity decreased by 74.7 μeq kg™1. As a result, the alkalinity/DIC ratio decreased from 1.07 in spring to 1.01 in summer and pH also decreased from 7.91 to 7.48, which resulted in the summertime undersaturation of the bottom waters.

Nutrient and Phytoplankton Analysis of a Mediterranean Coastal Area

Identifying and quantifying the key anthropogenic nutrient input sources are essential to adopting management measures that can target input for maximum effect in controlling the phytoplankton biomass. In this study, three systems characterized by distinctive main nutrient sources were sampled along a Mediterranean coast transect. These sources were groundwater discharge in the Ahuir area, the Serpis river discharge in the Venecia area, and a submarine wastewater outfall 1,900 m from the coast. The study area includes factors considered important in determining a coastal area as a sensitive area: it has significant nutrient sources, tourism is a major source of income in the region, and it includes an area of high water residence time (Venecia area) which is affected by the harbor facilities and by wastewater discharges. We found that in the Ahuir and the submarine wastewater outfall areas, the effects of freshwater inputs were reduced because of a greater water exchange with the oligotrophic Mediterranean waters. On the other hand, in the Venecia area, the highest levels of nutrient concentration and phytoplankton biomass were attributed to the greatest water residence time. In this enclosed area, harmful dinoflagellates were detected (Alexandrium sp. and Dinophysis caudata). If the planned enlargement of the Gandia Harbor proceeds, it may increase the vulnerability of this system and provide the proper conditions of confinement for the dinoflagellate blooms' development. Management measures should first target phosphorus inputs as this is the most potential-limiting nutrient in the Venecia area and comes from a point source that is easier to control. Finally, we recommend that harbor environmental management plans include regular monitoring of water quality in adjacent waters to identify adverse phytoplankton community changes.

Effects of freshwater inputs on the lower trophic levels of a temperate estuary: physical, physiological or trophic forcing?

The aim of this 6 year study was to assess whether freshwater inputs (rainfall and dam discharges) were acting as physical, physiological or trophic forcing factors on phytoplankton pigment concentrations and the dominant mysids of a temperate estuary (Guadalquivir estuary; SW, Spain). The effects of natural and human-controlled freshwater inputs modified the physico-chemical conditions and consequently biological production (bottom up control). Nutrient (nitrogen hypernutrification), suspended particulate matter and allochthonous photosynthetic pigment imports linked to freshwater inputs from adjacent habitats were observed, as well as light-limited autochthonous primary production. Seasonal and/or spatial patterns were shown by all study variables, including mysids. Freshwater management effects on dominant mysids differed depending on the species’ salinity tolerance (physiological forcing) and preferred prey availability (trophic forcing). Moreover, high inorganic matter content had a negative effect on the density of Mesopodopsis slabberi (physical forcing), which led to an increased detritivory/herbivory ratio (Neomysis integer/M. slabberi ratio). In conclusion, freshwater inputs appeared to effect estuarine lower trophic levels via a combination of different forcing mechanisms. Although several general patterns can be derived, the response of the system to freshwater inputs was not always univocal.

Effects of freshwater input on nutrient loading, phytoplankton biomass, and cyanotoxin production in an oligohaline estuarine lake

Pulsed river water events can increase nutrient levels potentially translating into enhanced primary production, phytoplankton community shifts, and bloom formation. The Bonnet Carre Spillway is a managed river diversion which can be used to redirect a significant amount of Mississippi River water into Lake Pontchartrain, reducing the risks of flood in the downstream communities during runoff seasons. We investigated nutrient enrichment and consequent changes in phytoplankton biomass, including toxic species in Lake Pontchartrain during and after a 1-month Bonne Carre Spillway opening in 2008. Water samples were collected along a 30 km transect. A freshwater plume was found to have formed by the strong river input that had limited mixing with the lake during the opening. The plume and lake water gradually mixed together after the Spillway was closed, indicated by the reduction of the horizontal salinity gradient. The river pulse increased the lake nitrate and dissolved reactive phosphorus concentrations to more than five times the lake background in the plume stations. Nutrient concentrations decreased rapidly after the Spillway closure as the plume dissipated. Diatoms and chlorophytes dominated the system during the opening. After the Spillway closure, there was a shift over time from diatom dominance to toxic cyanobacteria dominance that corresponded to more stable, warmer, and nutrient-limited water conditions. Associated toxins were present and varied over time and space. Further research on the phytoplankton assemblages on the lake is needed in subsequent, non-Spillway opening years to evaluate the impact of river water pulses on the development of these toxic cyanobacterial blooms.

Productivity and Distribution of Epipellic Microalgae Along Salinity Gradients in Mangrove Swamp of the Qua Iboe Estuary (NIGERIA)

Based on spatial variation in tidal mud salinity, direct gradient analysis procedures were adopted to relate the productivity and distribution of epipellic microalgae along salinity gradients in mangrove swamp of the Qua Iboe Estuary. Variations in mud salinities were due to distance from the coast, tidal incursions and freshwater input. The dilution effect of fresh water input from rainfall, urban runoff and associated freshwater creeks was most severe during the rainy season month of July, with much lower salinity levels recorded, in comparison to higher salinity values, recorded for same sampling locations during the drier month of December. In the dry season, all the microalgae species but Closterium (a genus of soft, green algae) and Oscillatoria (a cyanobacterium) species encountered in the tidal mud flats showed statistically significant negative correlations with salinity, while most microalgae species excluding Oscillatoria and Closterium species were positively correlated with the same factor during the wet season. Four Ecological Groups of microalgae, were established in the dry season month of December as against two Ecological Groups in the wet season month of July. However no microalgae species was found to occur on the highest values of mud salinity and there were overlapping range of occurrences and ecological optima for most species along the gradients.

Stratification, vertical mixing, and upward ammonium flux in hypersaline Mono Lake, California

The effects of freshwater inputs and wind on stratification, vertical mixing, and upward fluxes of ammonium were evaluated during 6-yr (1989-1994) of monomixis (one period of complete mixing a year) in hypersaline Mono Lake, California. Falling lake level (evaporation > freshwater inputs) during 5-yr led to unstable salinity (S) profiles (mixed-layer S > hypolimnetic S) over the period of strong thermal stratification (June-October). Profiles in October 1991 and 1994 indicate the occurrence of double diffusive salt fingering because of unstable salinity stratification. Stable salinity stratification persisted throughout the summer and delayed holomixis in 1993, the only year freshwater inputs were greater than evaporation. Biweekly to monthly eddy diffusivities (Kz) at the thermocline were estimated with the flux-gradient heat method corrected for solar heating. June-September K Z averages ranged from 9.5 x 10 -7 m 2 /s (SE = 4.8 x 10 -7 ) during wet 1993 (0.4 m lake level rise) to 4.2x10 -6 m 2 /s (SE = 1.9x10 -6 ) during the 1989 drought (0.6 m lake level decrease). The Lake Number, an index of seiche-induced mixing below the mixed-layer, explained 68 % of the variance in April-September metalimnetic diffusivities. Over the 6-yr 50-90 % of the seasonal (April-September) upward flux of ammonium was used or converted within the metalimnion likely from algal uptake and nitrification.