Anthropogenic impacts on the ecosystems of coastal lagoons: modelling fundamental biogeochemical processes and management implications

2004 ◽  
Vol 55 (1) ◽  
pp. 67 ◽  
Author(s):  
Ian T. Webster ◽  
Graham P. Harris
Keyword(s):  
Coastal Lagoon ◽  
Nutrient Loading ◽  
Anthropogenic Impacts ◽  
Coastal Lagoons ◽  
Alternative Stable States ◽  
Nitrogen Loading ◽  
Biogeochemical Model ◽  
Nutrient Loads ◽  
Stable States ◽  
Flushing Rate

This paper presents a biogeochemical model of a coastal lagoon intended to be representative of lagoons occurring along the south-east and south-west coasts of Australia. Many of these lagoons are threatened by increased nutrient loads because of land use change, by alterations to their freshwater inflows and by modification to their tidal flushing regimens. The model simulates the biogeochemical response of the lagoon to nutrient (nitrogen) loading and includes nutrient transformation processes in the sediments, as well as in the water column. The paper focuses on the response of primary producers to increasing and decreasing nutrient loads and how the response is altered by changes in the flushing rate of the lagoon with the sea. In common with lakes, the modelled lagoon exhibits alternative stable states representing macrophyte or phytoplankton dominance depending on nutrient loading and history. A third state representing severe degradation occurs when denitrification shuts down. A characteristic of Australian coastal lagoon systems is that, due to highly sporadic rainfall patterns, nutrient inflows are dominated by intermittent extreme events. The modelling demonstrates that such a loading regimen may be expected to generally increase the vulnerability of the lagoon to increasing nutrient loads. The results of the analysis presented are pertinent to several questions raised by coastal managers, such as what are the expected benefits of improving flushing by dredging and what are the consequences of altering the timing and magnitudes of the loads reaching the lagoons?

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

2017 ◽  
Vol 14 (19) ◽  
pp. 4423-4433 ◽  
Author(s):  
Yafei Zhu ◽  
Andrew McCowan ◽  
Perran L. M. Cook
Keyword(s):  
Water Quality ◽  
Primary Production ◽  
Total Phosphorus ◽  
Coastal Lagoon ◽  
Nutrient Dynamics ◽  
Nutrient Loading ◽  
Nitrogen Loading ◽  
Quality Model ◽  
Nitrogen Loads ◽  
Sediment Carbon

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.

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

2017 ◽  
Author(s):  
Yafei Zhu ◽  
Andrew McCowan ◽  
Perran L. M. Cook
Keyword(s):  
Water Quality ◽  
Coastal Lagoon ◽  
Nutrient Dynamics ◽  
Nutrient Loading ◽  
Phosphorus Release ◽  
Nitrogen Loading ◽  
Quality Model ◽  
Nitrogen Loads ◽  
Almost All ◽  
Sediment Carbon

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) was investigated using a 3D coupled hydrodynamic biogeochemical water quality model. The study showed that primary productivity 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 are the main drivers for the hypoxia and subsequent sediment phosphorus release in the Lake King. High primary production stimulated by large nitrogen loading brought by 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 TN and TP for water quality improvement in estuarine systems.

Community shifts, alternative stable states, biogeochemical controls and feedbacks in eutrophic coastal lagoons: a brief overview

2008 ◽  
Vol 18 (S1) ◽  
pp. S105-S117 ◽  
Author(s):  
Pierluigi Viaroli ◽  
Marco Bartoli ◽  
Gianmarco Giordani ◽  
Mariachiara Naldi ◽  
Sotiris Orfanidis ◽  
...  
Keyword(s):  
Coastal Lagoons ◽  
Alternative Stable States ◽  
Stable States ◽  
Community Shifts

scholarly journals A human impact metric for coastal ecosystems with application to seagrass beds in Atlantic Canada

FACETS ◽  
2019 ◽  
Vol 4 (1) ◽  
pp. 210-237 ◽  
Author(s):  
Grace E.P. Murphy ◽  
Melisa C. Wong ◽  
Heike K. Lotze
Keyword(s):  
Human Impact ◽  
Nutrient Loading ◽  
Human Impacts ◽  
Anthropogenic Impacts ◽  
Spatial Scales ◽  
Nitrogen Loading ◽  
Atlantic Canada ◽  
Seagrass Beds ◽  
Coastal Habitats ◽  
Coastal Bays

Coastal biogenic habitats are vulnerable to human impacts from both terrestrial and marine realms. Yet the broad spatial scale used in current approaches of quantifying anthropogenic stressors is not relevant to the finer scales affecting most coastal habitats. We developed a standardized human impact metric that includes five bay-scale and four local-scale (0–1 km) terrestrial and marine-based impacts to quantify the magnitude of anthropogenic impacts to coastal bays and nearshore biogenic habitats. We applied this metric to 180 seagrass beds ( Zostera marina), an important biogenic habitat prioritized for marine protection, in 52 bays across Atlantic Canada. The results show that seagrass beds and coastal bays exist across a wide human impact gradient and provide insight into which are the most and least affected by human threats. Generally, land alteration, nutrient loading, and shellfish aquaculture were higher in the Gulf of St. Lawrence, whereas invasive species and fishing activities were higher along the Atlantic coast. Sixty-four percent of bays were at risk of seagrass decline from nitrogen loading. We also found high within-bay variation in impact intensity, emphasizing the necessity of quantifying impacts at multiple spatial scales. We discuss implications for management and conservation planning, and application to other coastal habitats in Canada and beyond.

Alternative stable states in the aquatic vegetation of shallow urban lakes. II. Catastrophic loss of aquatic plants consequent to nutrient enrichment

2003 ◽  
Vol 54 (3) ◽  
pp. 201 ◽  
Author(s):  
Kay Morris ◽  
Paul C. Bailey ◽  
Paul I. Boon ◽  
Leesa Hughes
Keyword(s):  
Aquatic Plants ◽  
Nutrient Enrichment ◽  
Aquatic Vegetation ◽  
Nutrient Loading ◽  
Alternative Stable States ◽  
Nutrient Concentrations ◽  
Stable States ◽  
Nutrient Loadings ◽  
High Nutrient ◽  
Catastrophic Loss

The theory of alternative stable states predicts that high nutrient concentrations increase the probability of shallow lakes switching from a state dominated by vascular macrophytes to one dominated by phytoplankton and/or other algae. In the first paper of this series it was demonstrated that chronic, low-level nutrient loading did not affect a switch across vegetation states. To test the possibility that higher nutrient loadings result in vegetation changes, replicated mesocosms (~3000 L) were placed in an urban lake densely colonized by Vallisneria americana Michaux, a submerged angiosperm, and were subjected to higher levels of chronic nutrient enrichment. Moderate and high nutrient loadings significantly increased phytoplankton biomass and produced extensive, dense mats of floating algae. Many mesocosms became covered by the floating fern Azolla pinnata R.Br. This reduced light penetration and concentrations of dissolved oxygen in the water column profoundly and resulted in the complete loss of V. americana from almost all nutrient-enriched mesocosms within 4 months. A catastrophic loss of submerged aquatic plants so rapidly after nutrient enrichment is a relatively novel experimental finding, particularly in terms of the likely mechanism; that is, shading and subsequent anoxia caused by dense mats of floating plants other than algae.

scholarly journals A shady phytoplankton paradox: when phytoplankton increases under low light

2018 ◽  
Vol 285 (1882) ◽  
pp. 20181067 ◽  
Author(s):  
Masato Yamamichi ◽  
Takehiro Kazama ◽  
Kotaro Tokita ◽  
Izumi Katano ◽  
Hideyuki Doi ◽  
...  
Keyword(s):  
Species Interactions ◽  
Aquatic Ecosystems ◽  
Nutrient Loading ◽  
Scale Effects ◽  
Harmful Algal Bloom ◽  
Alternative Stable States ◽  
Ecosystem Dynamics ◽  
Light Limitation ◽  
Phytoplankton Abundance ◽  
Stable States

Light is a fundamental driver of ecosystem dynamics, affecting the rate of photosynthesis and primary production. In spite of its importance, less is known about its community-scale effects on aquatic ecosystems compared with those of nutrient loading. Understanding light limitation is also important for ecosystem management, as human activities have been rapidly altering light availability to aquatic ecosystems. Here we show that decreasing light can paradoxically increase phytoplankton abundance in shallow lakes. Our results, based on field manipulation experiments, field observations and models, suggest that, under competition for light and nutrients between phytoplankton and submersed macrophytes, alternative stable states are possible under high-light supply. In a macrophyte-dominated state, as light decreases phytoplankton density increases, because macrophytes (which effectively compete for nutrients released from the sediment) are more severely affected by light reduction. Our results demonstrate how species interactions with spatial heterogeneity can cause an unexpected outcome in complex ecosystems. An implication of our findings is that partial surface shading for controlling harmful algal bloom may, counterintuitively, increase phytoplankton abundance by decreasing macrophytes. Therefore, to predict how shallow lake ecosystems respond to environmental perturbations, it is essential to consider effects of light on the interactions between pelagic and benthic producers.

scholarly journals From heterotrophy to autotrophy: a freshwater estuarine ecosystem recovering from hypereutrophication

2009 ◽  
Vol 6 (3) ◽  
pp. 5431-5459 ◽  
Author(s):  
T. J. S. Cox ◽  
T. Maris ◽  
K. Soetaert ◽  
D. J. Conley ◽  
S. Van Damme ◽  
...  
Keyword(s):  
Algal Blooms ◽  
Alternative Stable States ◽  
Algal Growth ◽  
Nutrient Loads ◽  
Nutrient Inputs ◽  
Stable States ◽  
Estuarine Ecosystem ◽  
High Ammonia ◽  
Estuarine Systems ◽  
Algal Growth Inhibition

Abstract. Increased organic matter and nutrient loads have induced major changes in aquatic systems, including hypoxia and algal blooms. In enclosed ecosystems these changes were often not gradual due to non-linear mechanisms. Here we report a 40 year record of eutrophication and hypoxia on an estuarine ecosystem and its recovery from hypereutrophication. We observe a paradoxical increase in chlorophyll a concentrations with decreasing nutrient inputs, and we hypothesise that algal growth was inhibited due to hypereutrophication, either by elevated ammonium concentrations, severe hypoxia or the production of harmful substances in such a reduced environment. We study the dynamics of a simple but realistic mathematical model, incorporating the assumption of algal growth inhibition. It shows an autotrophic equilibrium with low ammonia inputs, and a heterotrophic equilibrium with high ammonia inputs. At intermediate ammonia inputs it displays two alternative stable states. We conclude that the recovery of hypereutrophic riverine/estuarine systems can exhibit threshold-like behaviour.

Fire Feedbacks with Vegetation and Alternative Stable States

2009 ◽  
Vol 18 (1) ◽  
pp. 159-173 ◽  
Author(s):  
Brian Beckage ◽  
Chris Ellingwood ◽  
Keyword(s):  
Alternative Stable States ◽  
Stable States ◽  
Fire Feedbacks
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