Effects of changes in nutrient loading and composition on hypoxia dynamics and internal nutrient cycling of a stratified coastal lagoon

Abstract

Abstract. The effects of changes in catchment nutrient loading and composition on the phytoplankton dynamics, development of hypoxia and internal nutrient dynamics in a stratified coastal lagoon system (the Gippsland Lakes) were investigated using a 3-D coupled hydrodynamic biogeochemical water quality model. The study showed that primary production was equally sensitive to changed dissolved inorganic and particulate organic nitrogen loads, highlighting the need for a better understanding of particulate organic matter bioavailability. Stratification and sediment carbon enrichment were the main drivers for the hypoxia and subsequent sediment phosphorus release in Lake King. High primary production stimulated by large nitrogen loading brought on by a winter flood contributed almost all the sediment carbon deposition (as opposed to catchment loads), which was ultimately responsible for summer bottom-water hypoxia. Interestingly, internal recycling of phosphorus was more sensitive to changed nitrogen loads than total phosphorus loads, highlighting the potential importance of nitrogen loads exerting a control over systems that become phosphorus limited (such as during summer nitrogen-fixing blooms of cyanobacteria). Therefore, the current study highlighted the need to reduce both total nitrogen and total phosphorus for water quality improvement in estuarine systems.

Early Diagenesis in Sediments of the Venice Lagoon (Italy) and Its Relationship to Hypoxia

“…Hypoxic conditions, in which dissolved oxygen (DO) concentration falls below 2 mg L −1 (62 µmol L −1 ), represent a major threat for coastal ecosystems worldwide (Zhang et al, 2010;Breitburg et al, 2018), because low levels of oxygen affects the metabolism and survival of the less mobile macrofauna (Rabalais et al, 2002;Vaquer-Sunyer and Duarte, 2008), and because the release of toxic compounds from sediments (e.g., H 2 S) can harm vertebrate species (Vaquer-Sunyer and Duarte, 2010). The interaction between sediment biogeochemistry and hypoxia has been thoroughly investigated in ecosystems where large areas are hypoxic or become periodically hypoxic (Diaz and Rosenberg, 2008;Middelburg and Levin, 2009), and is also receiving increasing attention in landlocked stratified environments (e.g., Friedrich et al, 2014;Zhu et al, 2017). Less attention has been given, however, to non-stratified shallow water systems where wind is expected to have a major role in water mixing and reoxygenation (Chapelle et al, 2000(Chapelle et al, , 2001.…”

Climate change overtakes coastal engineering as the dominant driver of hydrological change in a large shallow lagoon

“…Whilst nutrient loads are the primary determinant affecting the long-term trophic state of coastal waters (Howarth and Marino, 2006;Williamson et al, 2017), the timescales associated with water retention and mixing are critical in mediating the relationship between nutrient inputs and the ensuing water quality response, including the likelihood of nuisance algal blooms or hypoxia (e.g. Knoppers et al, 1991;Ferreira et al, 2005;Paerl et al, 2006;Zhu et al, 2017). The retention of water and hydrodynamic patterns that emerge in any given site are largely dependent upon local geomorphological features, though increasingly coastal engineering and changes in river hydrology disturb natural patterns of water exchange (Knoppers et al, 1991;Kjerfve et al, 1996;Dufour et al, 2001;Gong et al, 2008;Odebrecht et al, 2015;Almroth-Rosell et al, 2016).…”

Quantifying the Impact of Anthropogenic Atmospheric Nitrogen Deposition on the Generation of Hypoxia under Future Emission Scenarios in Chinese Coastal Waters

“…49,50 The East China Sea is one of the largest coastal oxygen-depleted regions globally and is simultaneously a major Chinese fishery. 50,51 Although river and groundwater discharge contributes to the high nutrient input to coastal waters in China, 52 atmospheric deposition also plays a key role in supplying N (Figure 1). 53−56 Because of industrialization, increased use of vehicles, and food production, 57 China is one of the largest emitters of anthropogenic N globally.…”

“…Eutrophication and seasonal hypoxia have been major environmental issues in China. − During the summer of 2006, a hypoxic zone of more than 15000 km 2 was reported in the East China Sea near the Yangtze River. , The East China Sea is one of the largest coastal oxygen-depleted regions globally and is simultaneously a major Chinese fishery. , Although river and groundwater discharge contributes to the high nutrient input to coastal waters in China, atmospheric deposition also plays a key role in supplying N (Figure ). − Because of industrialization, increased use of vehicles, and food production, China is one of the largest emitters of anthropogenic N globally .…”