Water Quality in Residential Tidal Canals

Abstract

Monitoring of water quality in residential tidal canals in Queensland has been carried out since 1974. Some recent data from four separate canal systems and their source waters is presented. Source water quality was generally good and this high quality was maintained in surface waters throughout these systems. Stratification of the water column in poorly flushed canal branches led to periodic deterioration in bottom water quality but this never resulted in significant management problems. Based on the Queensland data and on data from other Australian and overseas canal systems, conclusions are drawn about significant factors affecting canal water quality. These include flushing rates, source quality, polluting inputs, freshwater inflows and depth. Finally, possible objectives for canal water quality are discussed.

Potential implications of canal estates for nutrient budgets in coastal systems

“…Their construction has increased considerably worldwide in the past decades (Waltham & Connolly 2011). It has been shown that these modified estuaries receive high loads of land-derived nutrients, support high primary production rates, high OM deposition, and consequently promote changes in macrofauna structure (Cook et al 2007;Cosser 1989;Lemckert 2006;Maxted et al 1997;Morton 1989;Moss 1989). Accordingly, a number of concerns have arisen from the increase in the construction of these developments (Smith et al 1995); however, the potential threats they pose to coastal ecosystem nutrient cycling have been poorly addressed.…”

“…Another feature of these artificial waterways have a single or very few outlets connecting them to the outer estuary or open waters. Their design is typically long, narrow and deeper than the water source (Lindall & Trent 1976;Maxted et al 1997;Moss 1989). As a result, the tidal exchange with the water source is diminished, causing poor flushing and low flow of water.…”

“…Hydrodynamic studies have shown that the tidal flow decreases progressively towards the landward end of the canal estate, and dead-end canals are poorly flushed (Moss 1989). This causes bottom water currents to diminish, resulting in an accumulation of fine silts and biogenic materials towards the canal dead-end (Cook et al 2007;Cosser 1989;Lindall & Trent 1976;Morton 1989;Maxted et al 1997;Moss 1989;Nuttall & Richardson 1989;Reilly & Phillips 1998;Waltham & Conolly 2011).…”

“…Also, the more dense saline water layer sitting on the bottom presents a lower capacity to hold dissolved oxygen than the less dense lower saline surface waters. Complete anoxia may occur in some cases, particularly during the summer time (Atkins 1989;Lemckert 2006;Lindall et al 1975;Lindall & Trent 1976;Moss 1989).…”

“…As noted previously, the construction of artificial waterways has led to significant alteratio ns of some estuarine systems, and can potentially have profound impacts on the associated tidal creeks and wetlands (Cook et al 2007;Reilly & Phillips 1998). There have been some attempts to define the ecological role of these artificial waterways (Cosser 1989;Lemckert 2006;Maxted et al 1997;Morton 1989;Morton 1992;Moss 1989). However, there have been very few studies that elucidate the internal processes and attributes of these canal systems such that we still have a limited understanding of how they function relative to the ecosystems they replace.…”