Ecosystem thresholds with hypoxia

Conley, Daniel J.; Carstensen, Jacob; Vaquer-Sunyer, Raquel; Duarte, Carlos M.

doi:10.1007/978-90-481-3385-7_3

Cited by 39 publications

(38 citation statements)

References 39 publications

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“…Processes affected by hypoxia, such as denitrification and phosphorus retention, display thresholdlike behavior (Webster and Harris 2004;Conley et al 2009;Eyre and Ferguson 2009). Regime shifts, involving an abrupt change in ecosystem processes, can occur once specific thresholds of nutrient inputs are exceeded and this can cause changes in biological variables that propagate through several trophic levels (Conley et al 2009). The breakdown of coupled nitrification-denitrification and subsequent low DE, as well as the large flux of PO 4 3-from the sediments to the water column, suggests that thresholds have been exceeded in BC.…”

Section: Controls On Biogeochemical Processesmentioning

confidence: 98%

“…One of the most prominent effects of hypoxia is the increased P flux from sediments (Conley et al 2009). Phosphate fluxes are controlled by release from degradation of organic matter and by the buffering mechanism involving iron oxides at the sediment surface (Froelich 1988).…”

Section: Controls On Biogeochemical Processesmentioning

confidence: 99%

“…In the tidal creeks, the community respiratory quotient (CRQ = DIC/O 2 ) was -2 in the oligotrophic creeks and -4 in the hypereutrophic creek, indicating a shift to dominance of anaerobic mineralization processes with the increased nutrient loading in BC. This shift from aerobic to anaerobic metabolism occurs during hypoxic events, caused by excess nutrient inputs, and involves profound changes in the biogeochemical cycles of phosphorus and nitrogen (Conley et al 2009;Soetaert and Middelburg 2009).…”

Section: Controls On Biogeochemical Processesmentioning

confidence: 99%

“…Hypoxia is a common effect of nutrient loading in coastal marine ecosystems and the effects are most severe in areas such as shallow embayments or where tidal flushing is limited (Herbert 1999;Diaz and Rosenberg 2008). Hypoxia influences biogeochemical processes that control nutrient concentrations in the water column (Conley et al 2009) and can lead to dead zones which have serious consequences for ecosystem structure and functioning (Diaz and Rosenberg 2008). Thus, increased nutrient loads can have important consequences for the structure of estuarine communities, aquatic food webs and estuarine water quality.…”

Section: Introductionmentioning

confidence: 98%

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Effect of nutrient loading on biogeochemical processes in tropical tidal creeks

et al. 2011

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The effect of increased nutrient loads on biogeochemical processes in macrotidal, mangrovelined creeks was studied in tropical Darwin Harbour, Australia. This study uses an integrative approach involving multiple benthic and pelagic processes as measures of ecosystem function, and provides a comparison of these processes in three tidal creeks receiving different loads of treated sewage effluent. There were significant differences in process rates between Buffalo Creek (BC) (hypereutrophic), which receives the largest sewage loads; Myrmidon Creek (MC) (oligotrophic-mesotrophic) which receives smaller sewage inputs; and Reference Creek (RC) (oligotrophic) which is comparatively pristine.Benthic nutrient fluxes and denitrification were more than an order of magnitude higher and lower, respectively, in BC and denitrification efficiency (DE) was \10%. Pelagic primary production rates were also much higher in BC but respiration exceeded primary production resulting in severe drawdown of O 2 concentrations at night. Hypoxic conditions released oxide-bound phosphorus and inhibited coupled nitrification-denitrification, enhancing benthic nitrogen and phosphorus fluxes, leading to a build-up of excess nutrients in the water column. Poor water quality in BC was exacerbated by limited tidal flushing imposed by a narrow meandering channel and sandbar across the mouth. In contrast to BC, the effect of the sewage load in MC was confined to the water column, and the impact was temporary and highly localized. This is attributed to the effective flushing of the sewage plume with each tidal cycle. Denitrification rates in MC and RC were high (up to 6.83 mmol N m -2 day -1 ) and DE was approximately 90%. This study has identified denitrification, benthic nutrient fluxes and pelagic primary production as the biogeochemical processes most affected by nutrient loading in these tidal creek systems. Physical process play a key role and the combined influence of nutrient loading and poor tidal flushing can have serious consequences for ecosystem functioning.

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Section: Controls On Biogeochemical Processesmentioning

confidence: 98%

Section: Controls On Biogeochemical Processesmentioning

confidence: 99%

Section: Controls On Biogeochemical Processesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

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Effect of nutrient loading on biogeochemical processes in tropical tidal creeks

et al. 2011

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“…6.2.2). Accordingly, the onset of recurring seasonal hypoxia at around 1900 AD can be at least partly attributed to the naturally increased vulnerability to deoxygenation, which alongside global warming and direct anthropogenic forcing irreversibly tipped the ecosystem over a threshold, inducing a regime shift commonly associated with coastal oxygen deficiency (e.g., Conley et al, 2009b).…”

Section: Progressive Intensification Of Hypoxia During the Modern Warmentioning

confidence: 99%

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

et al. 2018

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Abstract. The anthropogenically forced expansion of coastal hypoxia is a major environmental problem affecting coastal ecosystems and biogeochemical cycles throughout the world. The Baltic Sea is a semi-enclosed shelf sea whose central deep basins have been highly prone to deoxygenation during its Holocene history, as shown previously by numerous paleoenvironmental studies. However, long-term data on past fluctuations in the intensity of hypoxia in the coastal zone of the Baltic Sea are largely lacking, despite the significant role of these areas in retaining nutrients derived from the catchment. Here we present a 1500-year multiproxy record of near-bottom water redox changes from the coastal zone of the northern Baltic Sea, encompassing the climatic phases of the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA), and the Modern Warm Period (MoWP). Our reconstruction shows that although multicentennial climate variability has modulated the depositional conditions and delivery of organic matter (OM) to the basin the modern aggravation of coastal hypoxia is unprecedented and, in addition to gradual changes in the basin configuration, it must have been forced by excess human-induced nutrient loading. Alongside the anthropogenic nutrient input, the progressive deoxygenation since the beginning of the 1900s was fueled by the combined effects of gradual shoaling of the basin and warming climate, which amplified sediment focusing and increased the vulnerability to hypoxia. Importantly, the eutrophication of coastal waters in our study area began decades earlier than previously thought, leading to a marked aggravation of hypoxia in the 1950s. We find no evidence of similar anthropogenic forcing during the MCA. These results have implications for the assessment of reference conditions for coastal water quality. Furthermore, this study highlights the need for combined use of sedimentological, ichnological, and geochemical proxies in order to robustly reconstruct subtle redox shifts especially in dynamic, non-euxinic coastal settings with strong seasonal contrasts in the bottom water quality.

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Dynamics of oxygen depletion in the nearshore of a coastal embayment of the southern Benguela upwelling system

Pitcher

Probyn²,

Randt³

et al. 2014

J. Geophys. Res. Oceans

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Acquisition of high resolution time series of water column and bottom dissolved oxygen (DO) concentrations inform the dynamics of oxygen depletion in St Helena Bay in the southern Benguela upwelling system at several scales of variability. The bay is characterized by seasonally recurrent hypoxia (<1.42 ml l 21 ) associated with a deep pool of oxygen-depleted water and episodic anoxia (<0.02 ml l 21 ) driven by the nearshore (<20 m isobath) decay of red tide. Coastal wind forcing influences DO concentrations in the nearshore through its influence on bay productivity and the development of red tides; through shoreward advection of the bottom pool of oxygen-depleted water as determined by the upwelling-downwelling cycle; and through its control of water column stratification and mixing. A seasonal decline in bottom DO concentrations of 1.2 ml l 21 occurs with a concurrent expansion of the bottom pool of oxygen depleted water in St Helena Bay. Upwelling of this water into the nearshore causes severe drops in DO concentration (<0.2 ml l 21 ), particularly during end-of-season upwelling, resulting in a significant narrowing of the habitable zone. Episodic anoxia through the entire water column is caused by localized degradation of red tides within the confines of the shallow nearshore environment. Oxygenation of the nearshore is achieved by ventilation of the water column particularly with the onset of winter mixing. No notable changes are evident in comparing recent measures of bottom DO concentrations in St Helena Bay to data collected in the late 1950s and early 1960s.

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Ecosystem thresholds with hypoxia

Cited by 39 publications

References 39 publications

Effect of nutrient loading on biogeochemical processes in tropical tidal creeks

Effect of nutrient loading on biogeochemical processes in tropical tidal creeks

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

Dynamics of oxygen depletion in the nearshore of a coastal embayment of the southern Benguela upwelling system

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