Global Dam‐Driven Changes to Riverine N:P:Si Ratios Delivered to the Coastal Ocean

Maavara, Taylor; Akbarzadeh, Zahra; Cappellen, Philippe Van

doi:10.1029/2020gl088288

Cited by 58 publications

(29 citation statements)

References 59 publications

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“…However, the volume of greenhouse gas produced during organic matter decomposition (CO 2 and CH 4 ) and through denitrification (N 2 O) remains undocumented for the SS reservoir. Our results are inline with [47], who proposed that dam-driven changes to nutrient stoichiometry operate in conjunction with other anthropogenic influences and modify ecosystem structure and functions.…”

Section: Implications For Coastal Productivitysupporting

confidence: 91%

“…Denitrification rates in the water column can be affected by nitrate availability, water temperature, organic carbon content, and dissolved oxygen [7]. Globally, reservoirs emit 3.7 Tg N year −1 as N 2 gas via denitrification, bury 1.54 Tg N year −1 in sediments and nitrification fix 0.98 Tg N year −1 [47] and reference therein).…”

Section: Biological Consumption and Change In Nutrient Ratiomentioning

confidence: 99%

“…Besides, studies proposed mechanism of nutrient removal in the reservoirs. Various studies quantified the relative importance of various processes resulting in removal of DIN (i.e., [2,31]), DIP [49,76] and DSi [21,35] in reservoirs and its impact on biogeochemical cycling [47]. It is important as riverine supply of nutrients, such as DIN, DIP, DSi and carbon (C) form basis for marine food webs.…”

Section: Introductionmentioning

confidence: 99%

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Nutrient retention behind a tropical mega-dam: a case study of the Sardar Sarovar Dam, India

et al. 2021

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In this study, we demonstrate the impact of the construction of a mega-dam on the nutrient export regime of a large tropical river into the Arabian Sea. Long-term (11 years) fortnight nutrient parameters, upstream and downstream to Sardar Sarovar (SS) Dam, were examined to determine the periodical change in nutrient fluxes from the Narmada River, India. During this 11-year period, the average discharge of the Narmada River upstream to Rajghat (35.3 km3 year−1) was higher than that of downstream at Garudeshwar (33.9 km3 year−1). However, during the same period, the suspended sediment load was reduced by 21 million tons (MT) from 37.9 MT at Rajghat to 16.7 MT at Garudeshwar. Similarly, mean concentrations of dissolved silica (DSi) reduced from 470 (upstream) to 214 µM (downstream), dissolved inorganic phosphate (DIP) from 0.84 to 0.38 µM, and dissolved inorganic nitrogen (DIN) from 43 to 1.5 µM. It means that about 54%, 55%, and 96% flux of DSi, DIP, and DIN retained behind the dam, respectively. The estimated denitrification rate (80,000 kg N km−2 year−1) for the reservoir is significantly higher than N removal by lentic systems, globally. We hypothesize that processes such as biological uptake and denitrification under anoxic conditions could be a key reason for the significant loss of nutrients, particularly of DIN. Finally, we anticipated that a decline in DIN fluxes (by 1.13 × 109 mol year−1) from the Narmada River to the Arabian Sea might reduce the atmospheric CO2 fixation by 7.46 × 109 mol year−1.

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Section: Implications For Coastal Productivitysupporting

confidence: 91%

Section: Biological Consumption and Change In Nutrient Ratiomentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Nutrient retention behind a tropical mega-dam: a case study of the Sardar Sarovar Dam, India

et al. 2021

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“…Overall the impacts of current hydropower facilities on nutrient transport were not large, and in most cases were not distinguishable based on comparisons between samples taken upstream and downstream of the facilities. This contrasts with the well-documented retention of N and P by larger reservoirs around the world (Maavara et al, 2020). As we hypothesized at the outset, the short water residence times of most of the reservoirs associated with SHPs likely explain their tendency to have little or no detectable effect on nutrient transport.…”

Section: Discussioncontrasting

confidence: 60%

Further Development of Small Hydropower Facilities May Alter Nutrient Transport to the Pantanal Wetland of Brazil

Oliveira

Fantin-Cruz

Campos

et al. 2020

Front. Environ. Sci.

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Small hydropower (SHP) facilities, defined variably but usually by installed capacities of <10–50 MW, are proliferating around the world, particularly in tropical and subtropical regions. Compared to larger dams, SHPs are generally viewed as having less environmental impact, although there has been little research to support that assertion. Numerous SHPs have been built, and many more are in development or proposed, in rivers that drain into the Pantanal, a world-renowned floodplain wetland system located mostly in Brazil. The upland tributaries are important sources of nutrients to the Pantanal, affecting the biological productivity of downstream floodplains. This study presents measurements from upstream and downstream of 25 current hydropower facilities, most of which are SHPs, throughout the upland watersheds of the Upper Paraguay River basin to reveal how these facilities may affect the concentrations and transport of nutrients in rivers flowing to the Pantanal. Artificial neural network models estimated the impact of building 80 future SHPs on nutrient transport into the Pantanal, based on observations at current facilities as well as the spatial distribution of future facilities. Overall impacts of current hydropower facilities were not large, and in most cases were indistinguishable based on comparisons between upstream and downstream. The short water residence times of reservoirs associated with SHPs likely explain their tendency to have little or no effect on nutrient transport. However, model predictions for hydropower facilities that may be built in the future, many on rivers with higher discharge and sediment loads, point to significant reductions in overall TN (8%) and TP (29%) transport, with potential negative consequences for river and floodplain productivity. Negative impacts may be either because the rivers carry low nutrient concentrations and are thereby sensitive to oligotrophication, or they are particularly important overall nutrient sources supporting ecosystem productivity in downstream rivers and floodplains. Together with a parallel study of sediment transport, these results support recommendations that several river systems presently lacking dams in their lower reaches should be excluded from future hydropower development to maintain the nutrient and sediment supply to the Pantanal.

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“…Moreover, the damming of rivers obstructs sediments transports delivery to the coastal zones, depriving the ecosystems from the minerals and nutrients they carry. Maavara et al 57 ecological model prediction for the midcentury, suggests that more than half of the worldwide rivers flowing to the sea will experience greater removal of silicon over nitrogen and phosphorus, as a consequence of increasing constructions of hydroelectric dams. The above have an impact on the role of diatoms in nearshore marine production, as they are increasingly outcompeted by other, potentially harmful, algae that do not need silicon to grow 57 .…”

Section: Origins and Implications Of The Coastal Vulnerabilitymentioning

confidence: 99%

Alarming coastal vulnerability of the deltaic and sandy beaches of North Africa

Hzami

Heggy

Amrouni

et al. 2021

Sci Rep

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The arid coasts of North Africa, extending over 4633 km from the Gulf of Tunis to the Nile Delta, are undergoing pronounced shoreline retreats and coastal floodings that are reported as a consequence of the ongoing sea level rise resulting from global warming. Of particular interest are the abnormal shoreline dynamics for deltaic and sandy beaches, which are severely impacted by abrupt decadal variabilities in both climatic and anthropogenic drivers resulting in their increased vulnerability to disturbances from coastal hazards. Unfortunately, the evolution, distribution and impacts of these drivers remain largely unquantified, let alone understood, for these extensive arid coasts that harbor the major portion of North Africa’s population as well as unique and fragile marine ecosystems. To address this deficiency, we use GIS-based multi-criteria approaches combined with analytic hierarchy process to map the Coastal Vulnerability Index and the Socioeconomic Vulnerability Index along these coasts to investigate the amplitude and extent of shoreline deterioration resulting from sudden fluctuations in sediment transport to the coastline. We use the western bay of the Gulf of Tunis, the coasts of Tripoli and the Nile Delta as three validation sites for our vulnerability assessment. The statistical Integrated Coastal Vulnerability Index map reveals that 47% of arid North African coasts are characterized by high to very high vulnerability. In particular, we observe that the densely populated deltaic coasts in both Tunisia and Egypt are 70% more vulnerable than any others coast in the eastern Mediterranean Basin. These abnormally high-vulnerability extensive areas are also correlated with significant deterioration of coastal aquifers and hence in crop production, compromising local food security and resulting in increasing outflow migration trends. Both Tunisia and Egypt observed dramatic increases in the net population outflow migration by respectively 62% and 248% between 2000 and 2016, mostly from coastal areas. Our source analysis of the amplitude and extent of these high coastal vulnerabilities suggests that they result from the anthropogenic drivers of damming and rapid urban growth over the last few decades rather than the effects of global warming.

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Global Dam‐Driven Changes to Riverine N:P:Si Ratios Delivered to the Coastal Ocean

Cited by 58 publications

References 59 publications

Nutrient retention behind a tropical mega-dam: a case study of the Sardar Sarovar Dam, India

Nutrient retention behind a tropical mega-dam: a case study of the Sardar Sarovar Dam, India

Further Development of Small Hydropower Facilities May Alter Nutrient Transport to the Pantanal Wetland of Brazil

Alarming coastal vulnerability of the deltaic and sandy beaches of North Africa

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