Modeling sources of nutrients in rivers draining into the Bay of Bengal—a scenario analysis

Abstract

We model future trends in river export of nutrients to the Bay of Bengal, and the sources of this pollution. We focus on total nitrogen (TN), total phosphorus (TP), and dissolved silica (DSi) inputs to the Bay of Bengal Large Marine Ecosystem (BOB LME) in the years 2000, 2030, and 2050. In 2000, rivers exported 7.1 Tg N and 1.5 Tg P to the BOB LME. Three rivers (Ganges, Godavari, Irrawaddy) account for 75-80% of the total river export of N and P. For 2050, we calculate an increase in river export of N to 8.6 Tg, while P export stabilizes at the 2000 level. Future trends are the net effect of increasing river export of dissolved N (by 40%) and P (by 80%), and decreasing river export of particulate N and P. The increases in dissolved N and P loads are associated primarily with increased N and P losses from agriculture and sewage systems. The decreasing export of particulate N and P is associated with damming of rivers and increased human water consumption. There are large differences in nutrient export among rivers. Rivers draining into the western BOB LME generally export more N and P than eastern BOB LME rivers. Most N and P in western BOB LME rivers are from anthropogenic sources. Future increases in dissolved inorganic N and P (DIN and DIP) export can be large for individual rivers: up to more than a factor of five for DIP and more than a doubling for DIN. The calculated nutrient export ratios (N and P relative to DSi) indicate an increasing risk for blooms of non-siliceous algal species, which can potentially produce toxins and otherwise disrupt coastal ecosystems. Our results indicate that basin-specific management may be the most effective approach towards reducing the risk of coastal eutrophication in the BOB LME.

Global Change Can Make Coastal Eutrophication Control in China More Difficult

“…The MARINA approach (Strokal et al, ) was developed based on the Global NEWS ‐2 model (Mayorga et al, ). The Global NEWS ‐2 model has been calibrated and validated for rivers worldwide (Amin et al, ; Mayorga et al, ; Pedde et al, ; Strokal & Kroeze, ) and for large Chinese rivers (the Yellow, Yangtze and Pearl) (Strokal et al, ). We tested the sensitivity of model outputs to changes in selected model inputs and parameters (Figures SE1–SE4).…”

“…In many world regions, this has resulted in increasing nutrient inputs to rivers. These nutrients are transported by rivers to seas, causing coastal eutrophication (Amin et al, ; McCrackin et al, ; Pedde et al, ; Seitzinger et al, ).…”

Anthropogenic nitrogen inputs and impacts on oceanic N2O fluxes in the northern Indian Ocean: The need for an integrated observation and modelling approach

“…Some part of this increased nitrogen load on land is transported into the northern Indian Ocean's estuaries and coastal waters (e.g., Martin et al [2011]; Singh and Ramesh [2011]; Krishna et al [2016]) likely resulting in rapid increases in aquatic organic and inorganic nitrogen levels [Liu et al 2008]. Based on results from the Global Nutrient Export from WaterSheds (NEWS) model [Pedde et al 2017;Seitzinger et al 2010], we estimate that there was an ~50% (1.22 Tg N yr -1 ) increase in riverine dissolved nitrogen input into the northern Indian Ocean between 1970-2000, 87% of which was directed into the Bay of Bengal.…”

“…Nitrogen [Baker et al, 2017]. These discrepancies that can be partially explained by seasonal biases in the sampling or by the pH dependence of the nitrate and ammonium partitioning to the aerosol phase [Weber et al, 2016;Kanakidou et al, 2018].Riverine dissolved inorganic and organic nitrogen inputs were obtained from the NEWS model [Seitzinger et al, 2010;Pedde et al 2017] and other sources listed in Table 1. Table 1.…”

Increasing nitrogen export to sea: A scenario analysis for the Indus River

“…This study is also the first to analyze the future trends in river export of N by the Indus River Chinese rivers (Strokal et al, 2016) and the Global NEWS-2 (Global Nutrient Export from WaterSheds) model. Global NEWS-2 was calibrated and validated for rivers worldwide , and for rivers draining into the Bay of Bengal from the Indian continent (Amin et al, 2017;Pedde et al, 2017). Most of the model inputs for MARINA 1.0 in this study were from peer-reviewed papers, published projects and databases ( Figure B.1 in Appendix B).…”