Academic literature on the topic 'Intermittently closed and open lake or lagoon'

Intermittently closed and open lakes or Lagoons (ICOLLs) are characterised by entrance barriers that form or break down due to the action of wind, waves and currents until the ocean-lagoon exchange becomes discontinuous. Entrance closure raises a variety of management issues that are regulated by monitoring. In this paper, those issues are investigated, and an automated sensor solution is proposed. Based upon a static Lidar paired with an edge computing device. This solar-powered remote sensing device provides an efficient way to automatically survey the lagoon entrance and estimate the berm profile. Additionally, it estimates the dry notch location and its height, critical factors in the management of the lagoon entrances. Generated data provide valuable insights into landscape evolution and berm behaviour during natural and mechanical breach events.

While significant studies have been conducted in Intermittently Closed and Open Lakes and Lagoons (ICOLLs), very few have employed Lagrangian drifters. With recent attention on the use of GPS-tracked Lagrangian drifters to study the hydrodynamics of estuaries, there is a need to assess the potential for calibrating models using Lagrangian drifter data. Here, we calibrated and validated a hydrodynamic model in Currimundi Lake, Australia using both Eulerian and Lagrangian velocity field measurements in an open entrance condition. The results showed that there was a higher level of correlation (R2 = 0.94) between model output and observed velocity data for the Eulerian calibration compared to that of Lagrangian calibration (R2 = 0.56). This lack of correlation between model and Lagrangian data is a result of apparent difficulties in the use of Lagrangian data in Eulerian (fixed-mesh) hydrodynamic models. Furthermore, Eulerian and Lagrangian devices systematically observe different spatio-temporal scales in the flow with larger variability in the Lagrangian data. Despite these, the results show that Lagrangian calibration resulted in optimum Manning coefficients (n = 0.023) equivalent to those observed through Eulerian calibration. Therefore, Lagrangian data has the potential to be used in hydrodynamic model calibration in such aquatic systems.

Intermittently open/closed coastal lakes and lagoons (ICOLLs) are common in Australia. Isolation from the sea makes them susceptible to nutrient enrichment and pollution and many are considered degraded. Understanding of their ecology and the effects of anthropogenic activity is limited. Many lakes are kept open artificially to improve water quality and mitigate the effects of floods. The present study examined the relationship between multivariate and univariate patterns in higher taxa of meiobenthos and compared their densities and distributions in naturally open and closed lakes with those in managed lakes. The degree of correspondence between multivariate and univariate patterns was taxon and locality dependent. Differences in densities between types of lakes was not related to physical factors. Within lakes, meiobenthos generally correlated negatively with salinity and organic content, but positively with silt. Densities reflected the degree of isolation from the sea, but the influence of this factor varied among lakes within categories and between taxa. Most taxa were less abundant in isolated localities, such as the inner reaches of lakes and in closed lakes. Meiobenthos were more spatially variable in closed and in managed lakes. The influence of frequency and duration of closure on the ecology of coastal lakes is discussed.

A large proportion of estuaries along microtidal wave-dominated coastlines worldwide have entrances that intermittently close to the ocean when tidal currents and fluvial discharge are insufficient to erode sediment delivered onshore by waves. In this study, these systems are termed “intermittently open/closed estuaries” (IOCE) in order to include all estuaries which intermittently close to the ocean. IOCE do not fit neatly into existing generalized estuary classification models and have been traditionally recognized as a single estuary type that constitute a rare subset of wave-dominated estuaries. In this study, 111 estuaries in Victoria, Australia, are used to develop a classification model that delineates between different IOCE types. This was undertaken using historic aerial imagery and quantification of the estuary channel width, catchment area, lagoon dimensions and tidal prism derived from remotely sensed data. Field surveying of entrance morphology was undertaken for a subsample of 35 IOCE characteristic of each section of the coast and which had detailed entrance condition records. Using this subset, IOCE were classified into three distinct types using multiple methods of statistical delineation (non-metric multidimensional scaling, hierarchical cluster analysis and distribution analysis). These three types are: (1) Type A, the largest IOCE which both close and open infrequently but for the longest durations; (2) Type B, medium sized IOCE which open and close several times per year for weekly to monthly durations; and (3) Type C (tidal creeks), the smallest IOCE located specifically in high rainfall, mountainous catchments and which exist in a predominantly open state. The three types of IOCE showed an order of magnitude difference in entrance closure duration as controlled by variations in the catchment area, tidal prism volume, dimensions of the estuarine lagoon and the entrance channel at the mouth. The classification is also applicable to wave-dominated coastlines internationally where IOCE are present.

The term 'Intermittently Closed and Open Lake or Lagoon (ICOLL)' has been adopted in NSW to described wave dominated barrier estuaries with an intermittent connection to the ocean. ICOLLs can also be found in south east Queensland, south-west Western Australia, and some parts of Victoria and Tasmania, although they are not the dominant estuary type as in NSW. From an international perspective, ICOLLs are also found in South Africa, New Zealand, Mexico and the Atlantic coast of Brazil and Uruguay. Within NSW, ICOLLs are mostly located south of Sydney, due to the high wave activity and close proximity of the Great Dividing Range to the coast, which results in small coastal catchments and thus small fluvial and sediment runoff. The distinguishing difference between ICOLLs and other estuary types is the variable condition of their entrances, which also makes them the most sensitive type of estuary to human interference (HRC, 2002; Boyd et al., 1992). The sensitivity of ICOLLs to external inputs has been described in this thesis based on their morphometric characteristics, which includes their size, shape and predominant entrance condition. NSW ICOLLs exhibit a wide range of physical conditions. Some ICOLLs are rarely open to the ocean, while others are rarely closed. Also, some ICOLLs have experienced extensive development within their catchments, while some are located mostly or wholly within National Parks and other protected reserves. When closed, ICOLLs behave like terminal lakes, retaining and assimilating 100% of the external inputs delivered to the system. When open, tidal flushing assists with advection and dispersion of inputs, however, significant tidal attenuation across the entrance still limits opportunities for effective removal of pollutants. The majority of NSW ICOLLs are considered to be mostly closed (i.e., have a closed entrance for more than 60% of the time), while remaining ICOLLs tend to be mostly open (i.e., have a closed entrance for less than 20% of the time). Few ICOLLs have entrances that are open and closed for roughly equal proportions of time, thus resulting in a distinctive bimodal behaviour of entrance condition (i.e., mostly open or mostly closed). NSW ICOLLs tend to be mostly closed unless (i) the catchment is larger than 100km2, and/or (ii) the exposure of the entrance to ocean swell waves is less than 60 degrees and/or (iii) the entrance channel contains geomorphic controls (e.g. shallow bedrock outcrops). Unless opened artificially, ICOLLs will generally remain closed until a sufficient volume of catchment runoff accumulates within the waterway to increase water levels to a level that overtops (breaches) the entrance sand berm. Once breached, high velocity flows over the berm cause scour and the development of a formalised entrance channel, which increases exponentially until an optimum width and depth has been reached (determined by the hydrostatic head, geomorphic controls and tidal conditions at the time). Following entrance breakout and lowering of the lagoon level, sand is reworked back into the entrance under the influence of flood tides and wave processes. The environmental condition of ICOLLs has generally been assumed as being dependent on the state of the catchment and the associated input of nutrients (form and magnitude) to the system. Biogeochemical processes also are reported to influence the condition of ICOLLs, particularly denitrification, which is controlled by the organic load on the bed and the extent of benthic algae and macrophytic productivity. In addition to this, however, it is demonstrated that the predominant and prevailing entrance conditions (i.e. open or closed) also influence the physical, chemical and biological environments. ICOLLs are particularly susceptible to the impacts of future climate change. This thesis provides a description of expected impacts on NSW ICOLLs environments associated in response to future climate changes, based on a detailed appreciation of physical processes and their follow-on consequences. Impacts on ICOLLs are expected as a result of increasing sea level, altered rainfall patterns, and modified offshore wave climate. A survey of relevant government officials has revealed that more than 50% of NSW ICOLLs are artificially opened before water levels reach the height of the natural entrance sand berm. Artificial entrance opening is mostly carried out to mitigate inundation of public and/or private assets around ICOLL foreshores, such as roads, backyards, farming lands and on-site sewage (septic) systems. Truncation of the hydraulic regime of ICOLLs can modify other physical, chemical and biological processes, and can result in deleterious impacts such as the terrestrialisation of estuarine wetlands and foreshores. Few statutory environmental planning mechanisms protect ICOLLs from future degradation. This thesis has identified the key issues that potentially compromise ICOLL integrity and sustainability, which include the expected future population growth in coastal NSW (thus increasing pressure for intensification of development within ICOLL catchments), future climate change (particularly increases in sea level), and the increased demand for amenity, particularly during summer holiday periods (i.e. 'summer impacts'). A series of management models have been developed to address key issues. The models comprise a suite of strategies that target future development and existing management practices, through a range of new or modified planning instruments. Models for the future management of ICOLL entrances aim to prevent artificial openings in the long-term. This requires, however, the systematic relocation, raising or flood-proofing of public and private assets that have been established on land that is potentially subject to inundation. Increasing sea levels in the future will compound the need for improved entrance management. Pro-active, integrated and adaptive management strategies need to be implemented today to minimise the on-going conflict and potential for continued environmental degradation in the future.

The term 'Intermittently Closed and Open Lake or Lagoon (ICOLL)' has been adopted in NSW to described wave dominated barrier estuaries with an intermittent connection to the ocean. ICOLLs can also be found in south east Queensland, south-west Western Australia, and some parts of Victoria and Tasmania, although they are not the dominant estuary type as in NSW. From an international perspective, ICOLLs are also found in South Africa, New Zealand, Mexico and the Atlantic coast of Brazil and Uruguay. Within NSW, ICOLLs are mostly located south of Sydney, due to the high wave activity and close proximity of the Great Dividing Range to the coast, which results in small coastal catchments and thus small fluvial and sediment runoff. The distinguishing difference between ICOLLs and other estuary types is the variable condition of their entrances, which also makes them the most sensitive type of estuary to human interference (HRC, 2002; Boyd et al., 1992). The sensitivity of ICOLLs to external inputs has been described in this thesis based on their morphometric characteristics, which includes their size, shape and predominant entrance condition. NSW ICOLLs exhibit a wide range of physical conditions. Some ICOLLs are rarely open to the ocean, while others are rarely closed. Also, some ICOLLs have experienced extensive development within their catchments, while some are located mostly or wholly within National Parks and other protected reserves. When closed, ICOLLs behave like terminal lakes, retaining and assimilating 100% of the external inputs delivered to the system. When open, tidal flushing assists with advection and dispersion of inputs, however, significant tidal attenuation across the entrance still limits opportunities for effective removal of pollutants. The majority of NSW ICOLLs are considered to be mostly closed (i.e., have a closed entrance for more than 60% of the time), while remaining ICOLLs tend to be mostly open (i.e., have a closed entrance for less than 20% of the time). Few ICOLLs have entrances that are open and closed for roughly equal proportions of time, thus resulting in a distinctive bimodal behaviour of entrance condition (i.e., mostly open or mostly closed). NSW ICOLLs tend to be mostly closed unless (i) the catchment is larger than 100km2, and/or (ii) the exposure of the entrance to ocean swell waves is less than 60 degrees and/or (iii) the entrance channel contains geomorphic controls (e.g. shallow bedrock outcrops). Unless opened artificially, ICOLLs will generally remain closed until a sufficient volume of catchment runoff accumulates within the waterway to increase water levels to a level that overtops (breaches) the entrance sand berm. Once breached, high velocity flows over the berm cause scour and the development of a formalised entrance channel, which increases exponentially until an optimum width and depth has been reached (determined by the hydrostatic head, geomorphic controls and tidal conditions at the time). Following entrance breakout and lowering of the lagoon level, sand is reworked back into the entrance under the influence of flood tides and wave processes. The environmental condition of ICOLLs has generally been assumed as being dependent on the state of the catchment and the associated input of nutrients (form and magnitude) to the system. Biogeochemical processes also are reported to influence the condition of ICOLLs, particularly denitrification, which is controlled by the organic load on the bed and the extent of benthic algae and macrophytic productivity. In addition to this, however, it is demonstrated that the predominant and prevailing entrance conditions (i.e. open or closed) also influence the physical, chemical and biological environments. ICOLLs are particularly susceptible to the impacts of future climate change. This thesis provides a description of expected impacts on NSW ICOLLs environments associated in response to future climate changes, based on a detailed appreciation of physical processes and their follow-on consequences. Impacts on ICOLLs are expected as a result of increasing sea level, altered rainfall patterns, and modified offshore wave climate. A survey of relevant government officials has revealed that more than 50% of NSW ICOLLs are artificially opened before water levels reach the height of the natural entrance sand berm. Artificial entrance opening is mostly carried out to mitigate inundation of public and/or private assets around ICOLL foreshores, such as roads, backyards, farming lands and on-site sewage (septic) systems. Truncation of the hydraulic regime of ICOLLs can modify other physical, chemical and biological processes, and can result in deleterious impacts such as the terrestrialisation of estuarine wetlands and foreshores. Few statutory environmental planning mechanisms protect ICOLLs from future degradation. This thesis has identified the key issues that potentially compromise ICOLL integrity and sustainability, which include the expected future population growth in coastal NSW (thus increasing pressure for intensification of development within ICOLL catchments), future climate change (particularly increases in sea level), and the increased demand for amenity, particularly during summer holiday periods (i.e. 'summer impacts'). A series of management models have been developed to address key issues. The models comprise a suite of strategies that target future development and existing management practices, through a range of new or modified planning instruments. Models for the future management of ICOLL entrances aim to prevent artificial openings in the long-term. This requires, however, the systematic relocation, raising or flood-proofing of public and private assets that have been established on land that is potentially subject to inundation. Increasing sea levels in the future will compound the need for improved entrance management. Pro-active, integrated and adaptive management strategies need to be implemented today to minimise the on-going conflict and potential for continued environmental degradation in the future.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environmental and Applied Science
Full Text

Coastal waterbodies and their catchments have been highly modified, leading to altered flushing and eutrophication. Strategies to manage water flow to either maintain water levels or reduce salt-water intrusion and mitigate impacts to coastal waterbodies include engineering approaches such as the construction of surge barriers and river diversions and manipulation of sandbars. Climate change is increasingly impacting coastal waterbodies with predictions of increased drying and significant changes to rainfall patterns. Consequently, engineering management strategies are likely to increase, but it is unclear how biogeochemistry and benthic cycling in coastal waterbodies will be affected, and how to manage the likely eutrophication issues that ensue. Therefore, the aim of this project was to determine how organic matter and nutrients are transported and cycled within a heavily modified intermittently closed/open lakes and lagoons (ICOLL). The Vasse Wonnerup Wetland System (VWWS) is a modified eutrophic ICOLL in southwestern Australia. It has been managed for over 100 years and has multiple surge barriers, river diversions, an oxygenation plant, and an artificially managed sandbar. In addition, significant portions of the VWWS seasonally dry out, making it an ideal system to study the effects of climate change to coastal systems which are likely to experience similar modifications as the VWWS. Stable isotope analyses and mixing models showed that the particulate organic matter (POM) in the system is derived mainly from autochthonous sources (fringing vegetation and aquatic macrophytes). Similarly, compound-specific stable isotopes showed that the sources of dissolved organic matter (DOM) are mainly autochthonous and dominated by dissolved organic nitrogen (DON). The extremely low ( < detection limit) concentrations of dissolved inorganic nitrogen (DIN; nitrate and ammonium) in the basin water column suggests that DON is crucial to sustaining a DIN supply in the VWWS through decomposition and tight cycling between DON and DIN. Currently, national and international management guidelines focus on inorganic nutrient concentrations as indicators of unacceptable concentrations (trigger values) and management strategies are generally focused upon reducing allochthonous (external) dissolved inorganic nutrients (i.e., nitrate, ammonium, and phosphate). This study shows that the focus of management on inorganic nutrients may not be well placed in this type of system. Benthic flux experiments demonstrated that water column DO and seasonal drying of the sediment did not affect dissolved organic C, N or P fluxes significantly but did influence benthic metabolism with higher rates occurring in high water column DO conditions. Despite this, benthic metabolism remained anaerobic. Surprisingly, decreasing water column DO did not influence net greenhouse gas (GHG) emissions indicating increasing water column DO will not decrease GHG emissions. Oxygenation of the water column did increase N removal, with higher net N2 effluxes with increasing water column DO. Bioavailable nitrogen pools the water column were supplemented in low DO conditions by N2O, with consumption of N2O occurring during dark hours. The lack of significant effects from DO manipulation treatments on many of the measured nutrient species indicate that maintenance of water column oxic conditions, regardless of the concentrations are unlikely to be effective in promoting removal or storage of nutrients in eutrophic systems. Increasing drying out of coastal waterbodies will have impacts on benthic metabolism, however this issue may become system specific depending on sandbar and surge barrier management strategies influencing water levels. Overall, this study confirmed the importance of autochthonous OM contributions and cycling in an ICOLL, whilst highlighting the impacts of engineered modifications in this type of coastal waterbody and its catchment.

Research Doctorate - Doctor of Philosophy (PhD)
Intermittently Closed and Open Lakes and Lagoons (ICOLLs) are coastal waterbodies that have intermittent connection to the ocean due to the formation of a barrier across the entrance. Catchment development is a major cause of pollution and also a justification for artificial barrier openings, which can have an adverse effect on the flora and fauna of ICOLLs. In most cases barrier openings may not have a direct effect on the biota of ICOLLs, but they can affect the factors which may influence invertebrate faunal and fish assemblages. The overall aim of this study was to determine what factors may influence fish assemblages of Central Coast ICOLLs. In order to understand these factors the research looked at the general ecology of Central Coast ICOLLs, including their invertebrate faunal assemblages and environmental parameters that may influence them (Chapter 3). Vegetated habitats within Central Coast ICOLLs include Ruppia sp. and the algae Chara sp. and Entermorpha intestinalis that support an invertebrate fauna dominated by polychaetes, crustaceans and molluscs. No single environmental variable had a major influence in structuring the invertebrate faunal assemblages at all four Central Coast ICOLLs. However, salinity was a major influencing factor at Cockrone, Avoca and Terrigal Lagoons, with percentage sediment composition a major factor at Wamberal Lagoon. Recruitment processes of larval and juvenile fishes are also presumably influenced by the status of the barrier. Larval and juvenile fishes occurring in Central Coast ICOLLs and their adjacent surf zones were identified to determine if movement of various species occurs once the barrier has been opened (Chapter 4). In this study, larval and juvenile fishes were more abundant in Central Coast ICOLLs but had lower species richness compared to their adjacent surf zones. The dominant larval and juvenile fish species found in ICOLLs included Ambassis jacksoniensis (Terrigal Lagoon), Philypnodon grandiceps (Avoca and Wamberal Lagoons) Atherinosoma microstoma (Wamberal Lagoon) and Acanthopagrus australis (Cockrone Lagoon). Hyperlophus vittatus was the dominant species collected from the adjacent surf zones. In this study there were no significant changes in larval and juvenile fish assemblages in either habitat from before to after barrier openings. Although some marine spawning species such as A. australis were present it could not be determined if these species were recruited from adjacent surf zones or from within these ICOLLs themselves. In most cases, Central Coast ICOLLs are considered to be generally self-recuiting environments, not for all species, but for many of their resident species of fish. Chapter Five determined the effects environmental parameters have on influencing fish assemblages. Fish assemblages of Central Coast ICOLLs showed low species richness, but high abundances of particular species when sampled using seine nets and multi-panel gillnets.Acanthopagrus australis (Cockrone Lagoon), Atherinosoma microstoma (Avoca and Wamberal Lagoons) and Ambassis jacksoniensis (Terrigal Lagoon) were the numerically dominant fish species collected using seine nets. Mugil cephalus was the species which was overall most frequently collected by gill netting. Fish assemblages were shown to be significantly different between Central Coast ICOLLs, and in this case were not directly influenced by barrier openings except at Wamberal Lagoon. However, Terrigal Lagoon, which had more barrier openings over the study period, compared to the other three ICOLLs, did have a higher diversity of fishes, which indicates that frequent barrier openings can influence fish assemblages. The major environmental influence on fish assemblages collected by seine nets at Cockrone and Wamberal Lagoons was salinity, and water temperature at Avoca and Terrigal Lagoons. The major environmental influence on fish assemblages collected by multi-panel gill nets at Cockrone and Avoca Lagoons was salinity, and water temperature at Terrigal Lagoon and >212 μm percentage sediment grain size at Wamberal Lagoon. Also, stochastic factors in the times and durations of barrier openings may play a large part in determining the fish assemblages that may be present at any one time in individual ICOLLs. High abundances of fish and their isolation from the ocean for long periods can result in competition for limited food resources, along with the effects that barrier openings may have on these resources not being fully understood (Chapter 6). Gut contents for each dominant species examined were similar; however each fish species had a dietary preference for a particular taxonomic group. Amphipods were the main dietary component of Acanthopagrus australis and Atherinosoma microstoma, with zooplankton being the main dietary component of Ambassis jacksoniensis. Barrier openings had a significant effect on the diets of A. australis (in Cockrone Lagoon) and A. microstoma (in Wamberal Lagoon), but not for species examined from Avoca and Terrigal Lagoons. Trace metal concentrations in sediments of Central Coast and Near-South Coast ICOLLs and gonad and liver tissues of Mugil cephalus were determined (Chapter 7). In the six ICOLLs studied, trace metal concentrations in both sediments and fish tissues were found to be relatively low and below guideline levels. Concentration levels did not differ significantly when compared between near-pristine (Termeil and Meroo Lakes), modified (Avoca and Terrigal Lagoons) and extensively-modified (Cockrone and Wamberal Lagoons) ICOLLs. Trace metal concentrations in sediments were not influenced by barrier openings. This study has shown that ICOLLs which are located geographically close to each other generally do not have similar environmental characteristics or fish assemblages which can be attributed to varying levels of development and land use activities within their individual catchments.