Freshwater Wetlands: Ecology, Rehabilitation and 2 Management Chapter 2.1 — Ecology of urban freshwater wetlands • 53 2.1 Ecology of urban freshwater wetlands Dr Liza Miller Watershed Ecology 6/42 – 46 Waters Road, Cremore NSW Sydney 2090 Australia Abstract Wetlands in urban environments are subject to an array of anthropogenic disturbances leading to wetland degradation or a state of environmental change from what a wetland might be in a natural setting. This is largely because developed landscapes affect wetland condition through impacts emanating from surrounding uplands as well as the immediate area. In particular, urban landscapes influence nutrient and pollutant inputs through water deposition leading to issues such as eutrophication. Nonetheless, urban wetlands are often valued for their amenity as well as their environmental attributes. Recreation activities, including kayaking, sailing, and bird watching, contribute to wetland amenity. The environmental values of a wetland and human activities in and around a wetland pose a challenge for wetland managers. That is, natural processes, such as eutrophication, have to be managed to ensure that recreational activities can be maintained but human health is not adversely affected. As well, opportunities for native flora and fauna need consideration in order to promote wetland values for their recreational use. This chapter introduces wetland ecology and examines the impact of urban activities on wetland condition. Three Australian case studies are examined; the Dandenong wetland (Victoria), Lake Tuggeranong (Australian Capital Territory), and the Jerrabomberra wetlands (Australian Capital Territory). All three wetlands are constructed, and with the exception of the Dandenong Wetland, multiple uses need to be managed to promote their condition and manage human activities in and around the wetlands. Chapter 2.1 — Ecology of urban freshwater wetlands • 54 Introduction the characteristics of the local landscape, including the river reaches, the values of a wetland may vary. Wetlands in the Catchment For instance, a delta-based wetland, through which River catchments are areas that funnel water into a river runs, will fulfil more of a water – filter/flow flowing streams (Coenraads and Koivula 2007). At moderator function, while water bodies cut off higher altitudes, there might be thousands of these from an active river channel fulfil more of a role as small streams that join to form larger streams that sheltered habitats or refugia (Kleeman et al. 2008). eventually meet the dominant river (Coenraads and Wetlands Defined Koivula 2007). Rivers are dynamic systems. Their drainage patterns, channel, meander, alluvial fans Irrespective of the wetland type, a wetland is and delta constantly change; sometimes quite typically an area of land covered by shallow water. dramatically after flood events (Coenraads and A more formal definition is provided in chapter 2.2, Koivula 2007). as adopted by Ramsar Convention. Wetlands can be natural or artificial, permanent or temporary. Wetlands are usually associated with flowing The water in them can be still or flowing, and fresh, rivers and streams (Coenraads and Koivula brackish, or salty (Melbourne Water n.d.). Wetland 2007). They occur in areas of a catchment where areas are defined according to their depth, degree the water table is at or above the land surface and timing of inundation and often the degree of for prolonged periods, providing waterlogged brackishness. Functionally, wetlands can be divided conditions for aquatic biota. Wetland character, into three zones: or the assemblages of flora and fauna that influence wetland patterns and processes, is largely • Inlet zone. The inlet zone is where a river determined by its location in the landscape. That or creek meets the wetland. This zone slows is, whether they are associated with montane or water flows and enables larger sediment headwater environments, or floodplain or coastal particles carried in the water to settle and riverine environments. sink. Aquatic plants may also grow in the edges of this area and as such, are able to withstand The shape and extent of a wetland depends fast water flows. on the underlying topography, geology and its location in the landscape over a larger drainage • Macrophyte zone. The macrophyte zone basin. Montane wetlands are typically associated comprises of plants that are wholly or partly with headwater streams in mountainous regions inundated. Here plants trap nutrients, heavy (Kleeman et al. 2008). For instance, the Snowy metals, suspended solids and organic matter. Mountains has numerous small montane wetlands • Open water zone. The open water zone where snowmelt drains into low-lying areas, provides opportunities for finer particles to keeping them constantly saturated (Kleeman et settle out of the water column and sunlight al. 2008). These areas are important as they tend to kill pathogenic bacteria. Due to sunlight to distribute run-off over prolonged periods and and high nutrient levels, algal growth occurs support unique communities of plants and animals from time to time in this zone. Algae trap (Kleeman et al. 2008). the dissolved nutrients, which allows them Riverine wetlands typically form in lower reaches to either enter the food chain or settle to the of a river catchment where a larger river is bottom of the pond. characterised by extensive meandering channels that twist and turn through a broad alluvial Wetland Ecology floodplain. Many loops of these meanders have Hydrology been cut to form oxbow lakes or billabongs Wetland hydrology is dealt with in greater details and these, together with extensive marshes, in chapters 2.2 and 3.2 in this eBook. For the benefit form remnants of a river’s past active channel of this chapter a brief overview of hydrology is (Coenraads and Koivula 2007). Usually a billabong provided here. or oxbow remains isolated from its neighbouring river (Kleeman et al. 2008), but during floods the Many wetlands fulfil an important role in the billabong may form part of an active river channel landscape. Some wetland functions are (after (Kleeman et al. 2008). Toward the lower reaches of (Kleeman et al. 2008); a catchment, floodplain and coastal wetlands begin • Reduce or moderate river flow and enable to dominate lentic environments. Depending on sediments to settle; Chapter 2.1 — Ecology of urban freshwater wetlands • 55 • Trap sediment and nutrients; Wetland Health or Condition • Provide habitat for fish, birds, vegetation and Wetlands are among the most impacted and invertebrates; degraded of all ecological systems. A global • Provide refugia for migratory birdlife; and overview indicates that massive losses of wetlands have occurred worldwide and that the majority • Provide a resource area for recreation and of the remaining wetlands are degraded, or cultural events. under threat of degradation (Finlayson 2000). The A key factor influencing wetland condition and health or condition of wetlands and associated extent is the hydrology or water regimes that, in vegetation communities can be negatively turn, influence wetland functions or ecology as impacted by changes in salinity, sedimentation, mentioned previously. Wetland ecosystem health pollution, removal and destruction of wetland (including the vegetation) is generally dependent habitat, and altered wetting regimes. These on natural water regimes that may be highly threatening processes can impact on the fauna variable. The wetland water regimes include the directly, through direct toxic effects, or indirectly, following features (Boulton and Brock 1999a): for example, through the loss of suitable breeding, sheltering and feeding sites and isolation of species’ • Timing of water presence. For seasonal populations due to lack of water connectivity; wetlands within-year patterns are important particularly between floodplain wetlands and while among-year patterns and variability in their adjacent river system. These impacts and timing are relevant to temporary wetlands. threats can result in declines of aquatic biodiversity • Frequency of wetland filling and drying occurs. from these systems. Activities causing such These regimes can range from zero (permanent impacts are believed to be large-scale clearing of waters) to frequent filling and drying in shallow native vegetation, use of fertilisers and erosion wetlands many times a year. of agricultural land, and regulation of rivers for water supply and irrigation (Department of • Periods of inundation. Inundation can Conservation and Environment, and Office of the vary from days to years and vary within and Environment 1992). Other activities that potentially among wetlands. Rates of rise and fall may threaten wetlands are infilling, over-grazing by also be important. livestock, introduced species, littering and pollution • The area of inundation and depth of water (Department of Conservation and Environment, and in a wetland. Office of the Environment 1992). • Wetland variability. That is, the degree to Many naturally occurring wetlands in Australia are which these above features change at a range modified, through human-induced disturbance of time scales such as land use and water management. In turn the extent and type of native vegetation Variability of water regime is a driving factor associated with wetland ecosystems is largely influencing the physical, chemical and biological dependent on wetland hydrology. Factors such components of Australian wetlands (Boulton and as width of the fringing vegetation