Ecological response of an intermittently open lagoon to entrance opening regimes and catchment loads: a numerical study

Ecological model behaviour of an intermittently closed and open lake or lagoon (ICOLL) is analysed in order to assess the response to altered estuary forcings (catchment loads, opening regimes and lake depth), initial conditions and model parameters. Due to the low nutrient loads currently entering Smiths Lake NSW Australia, changes in the opening regime do not exhibit a strong estuarine response, however the system is sensitive to increased water depth and catchment loads. The water depth of the lagoon is shown to drive a switch from a seagrass to an algal dominated system at average depths greater than 7 m. Elevated loads (10×) of phosphorus entering the estuary increase the productivity of phytoplankton which is limited by phosphorus at lower loads. Moderate nutrient enrichment stimulates the production of seagrass, which is generally nitrogen limited and catchment loads are able to double without a decline in seagrass biomass. At elevated catchment loads, light limitation of seagrass occurs due to the increased plankton biomass and total suspended solids, and the system switches from seagrass dominated to algal dominated at loads above 5 mg N m −2 d −1 and 0.09 mg P m −2 d −1 . Increasing nutrient loads

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