The relationship between sediment and water quality, and riverine sediment loads in the wave-dominated estuaries of south-west Western Australia

2004 ◽  
Vol 55 (6) ◽  
pp. 581 ◽  
Author(s):  
L. C. Radke ◽  
I. P. Prosser ◽  
M. Robb ◽  
B. Brooke ◽  
D. Fredericks ◽  
...  
Keyword(s):  
Water Quality ◽  
Organic Matter ◽  
Soil Erosion ◽  
Organic Carbon ◽  
Water Column ◽  
Nitrogen And Phosphorus ◽  
Weathering Index ◽  
Sediment Loads ◽  
The Impact ◽  
Column Total

We examine surface sediment and water column total nutrient and chlorophyll a concentrations for 12 estuaries with average water depths <4 m, and calculated sediment loads ranging from 0.2 to 10.8 kg m−2 year−1. Sediment total nitrogen, phosphorus and organic carbon concentrations vary inversely with sediment loads due to: (i) the influx of more mineral-rich sediment into the estuaries; and (ii) increasing sediment sulfidation. Sediment total organic carbon (TOC) : total sulfur (TS) and TS : Fe(II) ratios correlated to sediment loads because enhanced sedimentation increases burial, hence the importance of sulfate reduction in organic matter degradation. Curvilinear relationships were found between a weathering index and organic matter δ13C in sediment, and sediment load. The rising phase of the curve (increasing weathering, lighter isotopic values) at low to intermediate loads relates to soil erosion, whereas regolith or bedrock erosion probably explains the declining phase of the curve (decreasing weathering, heavier isotopic values) at higher sediment loads. The pattern of change for water column total nutrients (nitrogen and phosphorus) with sediment loads is similar to that of the weathering index. Most water quality problems occur in association with soil erosion, and at sediment loads that are intermediate for the estuaries studied. Limited evidence is presented that flushing can moderate the impact of sediment loads upon the estuaries.

scholarly journals Organic matter mineralization and trace element post-depositional redistribution in Western Siberia thermokarst lake sediments

2011 ◽  
Vol 8 (11) ◽  
pp. 3341-3358 ◽  
Author(s):  
S. Audry ◽  
O. S. Pokrovsky ◽  
L. S. Shirokova ◽  
S. N. Kirpotin ◽  
B. Dupré
Keyword(s):  
Trace Elements ◽  
Organic Matter ◽  
Organic Carbon ◽  
Lake Sediments ◽  
Water Column ◽  
Western Siberia ◽  
Ecosystem Development ◽  
Thermokarst Lake ◽  
Fe And Mn ◽  
The Impact

Abstract. This study reports the very first results on high-resolution sampling of sediments and their porewaters from three thermokarst (thaw) lakes representing different stages of ecosystem development located within the Nadym-Pur interfluve of the Western Siberia plain. Up to present time, the lake sediments of this and other permafrost-affected regions remain unexplored regarding their biogeochemical behavior. The aim of this study was to (i) document the early diagenesic processes in order to assess their impact on the organic carbon stored in the underlying permafrost, and (ii) characterize the post-depositional redistribution of trace elements and their impact on the water column. The estimated organic carbon (OC) stock in thermokarst lake sediments of 14 ± 2 kg m−2 is low compared to that reported for peat soils from the same region and denotes intense organic matter (OM) mineralization. Mineralization of OM in the thermokarst lake sediments proceeds under anoxic conditions in all the three lakes. In the course of the lake development, a shift in mineralization pathways from nitrate and sulfate to Fe- and Mn-oxyhydroxides as the main terminal electron acceptors in the early diagenetic reactions was suggested. This shift was likely promoted by the diagenetic consumption of nitrate and sulfate and their gradual depletion in the water column due to progressively decreasing frozen peat lixiviation occurring at the lake's borders. Trace elements were mobilized from host phases (OM and Fe- and Mn-oxyhydroxides) and partly sequestered in the sediment in the form of authigenic Fe-sulfides. Arsenic and Sb cycling was also closely linked to that of OM and Fe- and Mn-oxyhydroxides. Shallow diagenetic enrichment of particulate Sb was observed in the less mature stages. As a result of authigenic sulfide precipitation, the sediments of the early stage of ecosystem development were a sink for water column Cu, Zn, Cd, Pb and Sb. In contrast, at all stages of ecosystem development, the sediments were a source of dissolved Co, Ni and As to the water column. However, the concentrations of these trace elements remained low in the bottom waters, indicating that sorption processes on Fe-bounding particles and/or large-size organo-mineral colloids could mitigate the impact of post-depositional redistribution of toxic elements on the water column.

scholarly journals Effect of Land Cultivation on Soil Nutrient Sedimentation in Water at Southern China

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Jianshuang Gao ◽  
Yuhe Zhang ◽  
Zhuangzhuang Qian ◽  
Shunyao Zhuang
Keyword(s):  
Water Quality ◽  
Organic Matter ◽  
Soil Erosion ◽  
Water Conservation ◽  
Southern China ◽  
Soil Nutrient ◽  
Nitrogen And Phosphorus ◽  
Nutrient Distribution ◽  
Significant Difference ◽  
Land Cultivation

Soil erosion associated with land cultivation exerts a great impact on ecological environment. Such an impact is specific of land, crop, tillage, management and so on. This study aimed to investigate the effects of crop cultivation on water quality by comparing nutrient distribution in the sediment at Southern China. Two sedimentation sites adjacent to the uncultivated (S1) and cultivated upland (S2) were selected and samples were analyzed. Results showed that soil pH decreased with the increasing depth above 20 cm and then kept relatively stable of the both sediments. Soil organic matter, nitrogen and phosphorus contents decreased with the increasing depth. There was no significant difference between two sediments in organic matter and nitrogen contents, but the total phosphorus and extractable phosphorus contents in S2 were much higher than that in S1. The data indicated that soil eroded from S2 could possess much high potential to deteriorate water quality. Nutrient sedimentation can reflect the history of soil erosion and provide useful information for sustainable soil management and water conservation through improving cultivation and tillage measures.

scholarly journals Organic matter mineralization and trace element post-depositional redistribution in Western Siberia thermokarst lake sediments

2011 ◽  
Vol 8 (4) ◽  
pp. 8845-8894
Author(s):  
S. Audry ◽  
O. S. Pokrovsky ◽  
L. S. Shirokova ◽  
S. N. Kirpotin ◽  
B. Dupré
Keyword(s):  
Trace Elements ◽  
Organic Matter ◽  
Organic Carbon ◽  
Lake Sediments ◽  
Water Column ◽  
Western Siberia ◽  
Ecosystem Development ◽  
Thermokarst Lake ◽  
Fe And Mn ◽  
The Impact

Abstract. This study reports the very first results on high-resolution sampling of sediments and their porewaters from three thermokarst (thaw) lakes representing different stages of ecosystem development located within the Nadym-Pur interfluve of the Western Siberia plain. Up to present time, the lake sediments of this and other permafrost-affected regions remain unexplored regarding their biogeochemical behavior. The aim of this study was to (i) document the early diagenesic processes in order to assess their impact on the organic carbon stored in the underlying permafrost, and (ii) characterize the post-depositional redistribution of trace elements and their impact on the water column. The estimated organic carbon (OC) stock in thermokarst lake sediments of 14 ± 2 kg m−2 is low compared to that reported for peat soils from the same region and denotes intense organic matter (OM) mineralization. Mineralization of OM in the thermokarst lake sediments proceeds under anoxic conditions in all the three lakes. In the course of the lake development, a shift in mineralization pathways was evidenced from nitrate and sulfate to Fe- and Mn-oxyhydroxides as the main terminal electron acceptors in the early diagenetic reactions. This shift was promoted by the diagenetic consumption of nitrate and sulfate and their gradual depletion in the water column due to progressively decreasing frozen peat lixiviation occurring at the lake's borders. Trace elements were mobilized from host phases (OM and Fe- and Mn-oxyhydroxides) and partly sequestered in the sediment in the form of authigenic Fe-sulfides. Arsenic and Sb cycling was also closely linked to that of OM and Fe- and Mn-oxyhydroxides. Shallow diagenetic enrichment of particulate Sb was observed in the less mature stages. As a result of authigenic sulfide precipitation, the sediments of the early stage of ecosystem development were a sink for water column Cu, Zn, Cd, Pb and Sb. In contrast, at all stages of ecosystem development, the sediments were a source of dissolved Co, Ni and As to the water column. However, the concentrations of these trace elements remained low in the bottom waters, indicating that sorption processes on Fe-bounding particles and/or large-size organo-mineral colloids could mitigate the impact of post-depositional redistribution of toxic elements on the water column.

SOURCE APPORTIONMENT AND RETENTION OF NUTRIENTS AND ORGANIC MATTER IN THE MERKYS RIVER BASIN IN SOUTHERN LITHUANIA/SKIRTINGŲ ŠALTINIŲ POVEIKIS BIOGENINIŲ IR ORGANINIŲ MEDŽIAGŲ PERNAŠAI IR SULAIKYMUI MERKIO UPĖS BASEINE PIETŲ LIETUVOJE/ РАСПРЕДЕЛЕНИЕ И ЗАДЕРЖАНИЕ БИОГЕННЫХ И ОРГАНИЧЕСКИХ ВЕЩЕСТВ В БАССЕЙНЕ РЕКИ MEРКИС В ЮЖНОЙ ЧАСТИ ЛИТВЫ

2008 ◽  
Vol 16 (4) ◽  
pp. 195-204 ◽  
Author(s):  
Arvydas Povilaitis
Keyword(s):  
Water Quality ◽  
Organic Matter ◽  
River Basin ◽  
Water Quality Monitoring ◽  
Point Sources ◽  
Anthropogenic Sources ◽  
Simultaneous Estimation ◽  
Successful Implementation ◽  
Nitrogen And Phosphorus ◽  
The Impact

The assessment of the type of human activity in a basin area that may cause an impact on the status of a water body is needed for successful implementation of the EU Water Framework Directive. Lack of necessary information often makes it difficult to perform the task. Therefore, the statistical MESAW model based on export coefficients approach has been used in this study for evaluation of the impact of different sources of nutrients and organic matter on the water quality in the Merkys River in southern Lithuania. The model was tested on the basis of data from 5 water quality monitoring sites with corresponding subbasin data on land use, point sources and atmospheric deposition. Nonlinear regression was used for simultaneous estimation of the export coefficients and retention. The results revealed that the impact of anthropogenic sources accounted for 73% of COD, 56% of BOD, 90% of Ntot and 78% of Ptot loads measured in the Merkys River. Forest and wetlands contribute from 9.5 to 44% to the corresponding load. The retention in the Merkys River, Basin was found to be high for nitrogen and phosphorus and low for organic matter. Santrauka Įgyvendinant vandensaugos uždavinius turi būti įvertintas konkretaus upės baseino vandens taršos lygis ir numatytos priemonės, padėsiančios pasiekti gerą būklę. Kiekvienos upės baseinas yra sudėtinga ekosistema, kurioje susipina gamtiniai ir antropogeniniai veiksniai. Jie veikia kompleksiškai, todėl analizuojant vandens terpėje migruojančias medžiagas sunku įvertinti kiekvieno jų įtaką. Gamtinių ir antropogeninių veiksnių poveikiui biogeninių ir organinių medžiagų srautams bei jų sulaikymui Merkio upės baseine įvertinti buvo pritaikytas statistinis MESAW modelis. Jis pagrįstas emisijos koeficientų nustatymu įvertinant baseino žemėnaudą, taškinius taršos šaltinius ir atmosferines iškritas. Taikant netiesinės regresijos metodus nustatytas skirtingų veiksnių poveikis upės vandens kokybei. Rezultatai parodė, kad antropogeninių šaltinių poveikis sudaro 73 % ir 56 % (pagal ChDSCr ir BDS7 ) bendro pernešamo organinių medžiagų kiekio Merkio upėje. Žmogaus veikla lemia 90 % pernešamo metinio bendrojo azoto ir 78 % bendrojo fosforo kiekio. Miško poveikis biogeninių ir organinių medžiagų srautams sudaro nuo 9,5 % iki 44 %. Bendrojo azoto ir bendrojo fosforo sulaikymas upės baseine siekia 79 % ir 64 %. Organinių junginių sulaikymas mažas – 9,7 % pagal BDS7 ir 42,3 % pagal ChDSCr. Резюме При решении задач по водоохране должна быть учтена степень загрязненности воды каждого конкретного бассейна реки и намечены меры по улучшению его состояния. Бассейн каждой реки является сложной экосистемой, на которую комплексное воздействие оказывают разные природные и антропогенные факторы, определить влияние каждого из которых довольно трудно. Для оценки воздействия природных и антропогенных факторов на потоки биогенных и органических веществ и их задержание в бассейне реки Меркис была применена статистическая модель MESAW, основанная на определении коэффициентов эмиссии. Результаты показали, что воздействие антропогенных источников составляет 73% общeго объемa химического потребления кислородa (XпK), 56% биохимического потребления кислородa (бпK), 90% общeго количества азота и 78% общeго количества фосфора, измеренных в реке. Воздействие лесов и болот на поток биогенных и органических веществ составляет от 9,5% до 44% общeго объемa веществ. Было устaнoвлeнo, что в бассейне реки Meркис задерживается много азота (79%) и фосфора (64%) и мало органического вещества (9.7–42.3%).

Fish farming in Denmark: environmental impact of regulative legislation

1995 ◽  
Vol 31 (10) ◽  
pp. 73-84 ◽  
Author(s):  
T. M. Iversen
Keyword(s):  
Organic Matter ◽  
Environmental Impact ◽  
Freshwater Fish ◽  
Aquatic Environment ◽  
Action Plan ◽  
Fish Farming ◽  
Fish Farms ◽  
Nitrogen And Phosphorus ◽  
Local Impact ◽  
The Impact

The main environmental problems associated with fish farming in Denmark are attributable to the dam, the “dead reach” and nutrient and organic matter discharge. The environmental regulation of fish farming in Denmark started with the Environmental Protection Act of 1974, the Statutory Order of 1985 forbidding wet feed, and the Action Plan on the Aquatic Environment of 1987. In the case of freshwater fish farms, the latter was implemented through the measures stipulated in the 1989 Statutory Order on Fish Farms. The impact of Danish legislative measures to reduce and regulate the environmental effects of freshwater fish farms can be summarized as follows: - the number of fish farms has been reduced from about 800 in 1974 to about 500 at present; - production has tripled since 1974 and has been stable since 1989; - a change from wet to dry feed has reduced the environmental impact of the farms; - the national goals of the Action Plan on the Aquatic Environment of 1987 for reducing fish farm discharges of organic matter, nitrogen and phosphorus have been fulfilled. The main remaining problems are that: - the local impact of fish farms on downstream stream quality is still much too high in about 15% of cases; - the problem of the passage of migrating invertebrates and fish is still unsolved at some farms; - the problems posed by “dead reaches” are still unsolved. It is concluded that sustainable fish farming is possible in Denmark, but with the present technology production will have to be significantly reduced.

Impact of vegetative cover and slope on runoff, erosion, and water quality for field plots on a range of soil and spoil materials on central Queensland coal mines

Soil Research ◽  
2000 ◽  
Vol 38 (2) ◽  
pp. 313 ◽  
Author(s):  
C. Carroll ◽  
L. Merton ◽  
P. Burger
Keyword(s):  
Water Quality ◽  
Soil Erosion ◽  
Overland Flow ◽  
Salt Content ◽  
Vegetative Cover ◽  
Rhodes Grass ◽  
Erosion Rates ◽  
Mine Sites ◽  
The Impact ◽  
Field Plots

In 1993, a field study commenced to determine the impact of vegetative cover and slope on runoff, erosion, and water quality at 3 open-cut coal mine sites. Runoff, sediment, and water quality were measured on 0.01-ha field plots from 3 slope gradients (10, 20, 30%), with pasture and tree treatments imposed on soil and spoil material, and 2 soil and spoil plots left bare. The greatest soil erosion occurred before pasture cover established, when a large surface area of soil (>0.5 plot area) was exposed to rainfall and overland flow. Once buffel grass (Cenchrus ciliaris) colonised soil plots, there were negligible differences in soil erosion between slope gradients. On spoil, Rhodes grass (Chloris gayana) reduced in situ soluble salt content, and reduced runoff electrical conductivity to levels measured in surrounding creeks. Where spoil crusted there was poor vegetative growth and unacceptably large runoff and erosion rates throughout the study.

Effects of Fe addition on sediment P dynamics in a eutrophic lake

2021 ◽  
Author(s):  
Melanie Münch ◽  
Rianne van Kaam ◽  
Karel As ◽  
Stefan Peiffer ◽  
Gerard ter Heerdt ◽  
...  
Keyword(s):  
Water Quality ◽  
Organic Matter ◽  
Surface Water ◽  
Water Column ◽  
Sediment Cores ◽  
Surface Water Quality ◽  
Water Interface ◽  
Eutrophic Lakes ◽  
Fe Addition

&lt;p&gt;The decline of surface water quality due to excess phosphorus (P) input is a global problem of increasing urgency. Finding sustainable measures to restore the surface water quality of eutrophic lakes with respect to P, other than by decreasing P inputs, remains a challenge. The addition of iron (Fe) salts has been shown to be effective in removing dissolved phosphate from the water column of eutrophic lakes. However, the resulting changes in biogeochemical processes in sediments as well as the long-term effects of Fe additions on P dynamics in both sediments and the water column are not well understood.&lt;/p&gt;&lt;p&gt;In this study, we assess the impact of past Fe additions on the sediment P biogeochemistry of Lake Terra Nova, a well-mixed shallow peat lake in the Netherlands. The Fe-treatment in 2010 efficiently reduced P release from the sediments to the surface waters for 6 years. Since then, the internal sediment P source in the lake has been increasing again with a growing trend over the years.&lt;/p&gt;&lt;p&gt;In 2020, we sampled sediments at three locations in Terra Nova, of which one received two times more Fe during treatment than the other two. Sediment cores from all sites were sectioned under oxygen-free conditions. Both the porewaters and sediments were analysed for their chemical composition, with sequential extractions providing insight into the sediment forms of P and Fe. Additional sediment cores were incubated under oxic and anoxic conditions and the respective fluxes of P and Fe across the sediment water interface were measured.&lt;/p&gt;&lt;p&gt;The results suggest that Fe and P dynamics in the lake sediments are strongly coupled. We also find that the P dynamics are sensitive to the amount of Fe supplied, even though enhanced burial of P in the sediment was not detected. The results of the sequential extraction procedure for P, which distinguishes P associated with humic acids and Fe oxides, as well as reduced flux of Fe(II) across the sediment water interface in the anoxic incubations, suggest a major role of organic matter in the interaction of Fe and P in these sediments.&lt;/p&gt;&lt;p&gt;Further research will include investigations of the role of organic matter and sulphur in determining the success of Fe-treatment in sequestering P in lake sediments. Based on these data in combination with reactive transport modelling we aim to constrain conditions for successful lake restoration through Fe addition.&lt;/p&gt;

Biogeochemical and ecological features of sinking particulate matter in the deep Ionian Sea (E. Mediterranean) during a 10-year time series study: impacts of atmospheric and oceanographic variabilities on carbon production and sequestration

2021 ◽  
Author(s):  
Alexandra Gogou ◽  
Constantine Parinos ◽  
Spyros Stavrakakis ◽  
Emmanouil Proestakis ◽  
Maria Kanakidou ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Organic Carbon ◽  
Carbon Cycle ◽  
Atmospheric Deposition ◽  
Water Column ◽  
Particulate Organic Carbon ◽  
Nutrient Dynamics ◽  
Ionian Sea ◽  
Ecological Features ◽  
The Impact

&lt;p&gt;Biotic and abiotic processes that form, alter, transport, and remineralize particulate organic carbon, silicon, calcium carbonate, and other minor and trace chemical species in the water column are central to the ocean&amp;#8217;s ecological and biogeochemical functioning and of fundamental importance to the ocean carbon cycle. Sinking particulate matter is the major vehicle for exporting carbon from the sea surface to the deep sea. During its transit towards the sea floor, most particulate organic carbon (POC) is returned to inorganic form and redistributed in the water column. This redistribution determines the surface concentration of dissolved CO&lt;sub&gt;2&lt;/sub&gt;, and hence the rate at which the ocean can absorb CO&lt;sub&gt;2&lt;/sub&gt; from the atmosphere. The ability to predict quantitatively the depth profile of remineralization is therefore critical to deciphering the response of the global carbon cycle to natural and human-induced changes.&lt;/p&gt;&lt;p&gt;Aiming to investigate the significant biogeochemical and ecological features and provide new insights on the sources and cycles of sinking particulate matter, a mooring line of five sediment traps was deployed from 2006 to 2015 (with some gap periods) at 5 successive water column depths (700, 1200, 2000, 3200 and 4300 m) in the SE Ionian Sea, northeastern Mediterranean (&amp;#8216;NESTOR&amp;#8217; site). We have examined the long-term records of downward fluxes for Corg, N&lt;sub&gt;tot&lt;/sub&gt;, &amp;#948;&lt;sup&gt;13&lt;/sup&gt;Corg and &amp;#948;&lt;sup&gt;15&lt;/sup&gt;N&lt;sub&gt;tot&lt;/sub&gt;, along with the associated ballast minerals (opal, lithogenics and CaCO&lt;sub&gt;3&lt;/sub&gt;), lipid biomarkers, Chl-a and PP rates, phytoplankton composition, nutrient dynamics and atmospheric deposition. &amp;#160;&lt;/p&gt;&lt;p&gt;The satellite-derived seasonal and interannual variability of phytoplankton metrics (biomass and phenology) and atmospheric deposition (meteorology and air masses origin) was examined for the period of the sediment trap experiment. Regarding the atmospheric deposition, synergistic opportunities using Earth Observation satellite lidar and radiometer systems are proposed (e.g. Cloud&amp;#8208;Aerosol Lidar with Orthogonal Polarization - CALIOP, Moderate Resolution Imaging Spectroradiometer - MODIS), aiming towards a four&amp;#8208;dimensional exploitation of atmospheric aerosol loading (e.g. Dust Optical Depth) in the study area.&lt;/p&gt;&lt;p&gt;Our main goals are to: i) develop a comprehensive knowledge of carbon fluxes and associated mineral ballast fluxes from the epipelagic to the mesopelagic and bathypelagic layers, ii) elucidate the mechanisms governing marine productivity and carbon export and sequestration to depth and iii) shed light on the impact of atmospheric forcing and deposition in respect to regional and large scale circulation patterns and climate variability and the prevailing oceanographic processes (internal variability).&lt;/p&gt;&lt;p&gt;Acknowledgments&lt;/p&gt;&lt;p&gt;We acknowledge support of this work by the Action &amp;#8216;National Network on Climate Change and its Impacts &amp;#8211; &lt;strong&gt;CLIMPACT&lt;/strong&gt;&amp;#8217;, funded by the Public Investment Program of Greece (GSRT, Ministry of Development and Investments).&lt;/p&gt;

scholarly journals Natural organic matter removal by ion exchange at different positions in the drinking water treatment lane

2013 ◽  
Vol 6 (1) ◽  
pp. 1-10 ◽  
Author(s):  
A. Grefte ◽  
M. Dignum ◽  
E. R. Cornelissen ◽  
L. C. Rietveld
Keyword(s):  
Water Quality ◽  
Drinking Water ◽  
Organic Matter ◽  
Water Treatment ◽  
Organic Carbon ◽  
Natural Organic Matter ◽  
Drinking Water Treatment ◽  
Biological Stability ◽  
Sand Filtration ◽  
Slow Sand Filtration

Abstract. To guarantee a good water quality at the customers tap, natural organic matter (NOM) should be (partly) removed during drinking water treatment. The objective of this research was to improve the biological stability of the produced water by incorporating anion exchange (IEX) for NOM removal. Different placement positions of IEX in the treatment lane (IEX positioned before coagulation, before ozonation or after slow sand filtration) and two IEX configurations (MIEX® and fluidized IEX (FIX)) were compared on water quality as well as costs. For this purpose the pre-treatment plant at Loenderveen and production plant Weesperkarspel of Waternet were used as a case study. Both, MIEX® and FIX were able to remove NOM (mainly the HS fraction) to a high extent. NOM removal can be done efficiently before ozonation and after slow sand filtration. The biological stability, in terms of assimilable organic carbon, biofilm formation rate and dissolved organic carbon, was improved by incorporating IEX for NOM removal. The operational costs were assumed to be directly dependent of the NOM removal rate and determined the difference between the IEX positions. The total costs for IEX for the three positions were approximately equal (0.0631 € m−3), however the savings on following treatment processes caused a cost reduction for the IEX positions before coagulation and before ozonation compared to IEX positioned after slow sand filtration. IEX positioned before ozonation was most cost effective and improved the biological stability of the treated water.

Consequences of nutrient load reductions for carbon and alkalinity dynamics within the region of freshwater influence of River Elbe

2021 ◽  
Author(s):  
Johannes Paetsch ◽  
Helmuth Thomas
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Sulfate Reduction ◽  
Biogeochemical Model ◽  
Time Interval ◽  
Nutrient Loads ◽  
Organic Matter Degradation ◽  
Strong Decrease ◽  
Nitrogen And Phosphorus ◽  
River Elbe

&lt;p&gt;Since the early eighties of the 20&lt;sup&gt;th&lt;/sup&gt; century nitrogen and phosphorus loads of the River Elbe, a river entering the North European Shelf at the southeastern coast, have decreased by a factor of about four. This resulted in a reduction of the eutrophication status in the adjacent German Bight and the coastal waters west of Denmark. In addition, benthic carbon and alkalinity pools have changed due to 1- changed carbon loads and, 2- changed decay pathways of benthic organic carbon.&lt;/p&gt;&lt;p&gt;We investigate the consequences of observed nutrient and organic loads by rivers with a 3D-biogeochemical model including a 3D-early diageneses model within the sediment for the time 1979 - 2014. &amp;#160;&amp;#160;&lt;/p&gt;&lt;p&gt;The results show a strong decrease of benthic carbon rather due to decreasing nutrient loads and subsequent autochthonous biological production than changes in organic loads. The export of inorganic carbon from the sediment is related to the magnitude of benthic organic carbon and cannot explain the strong decrease of the benthic POC pool.&amp;#160;During the time until the early nineties aerobic degradation increases, whereas denitrification and sulfate reduction as organic matter degradation pathway decreases.&lt;/p&gt;&lt;p&gt;Alkalinity production due to benthic organic matter degradation decreases over the first half of the investigated time interval and keeps constant during the second half. Denitrification and sulfate reduction dominate the mechanisms decreasing the alkalinity export. Benthic nitrification consuming alkalinity strongly increases during the first half of the time dampening the decrease of alkalinity export.&lt;/p&gt;

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