Quantifying flow habitat biota relationships in riverine ecosystems: Ecological response to manipulations of the hydrology in slackwater and flow patches on the Broken River, year 1 synthesis report

"November 2004".

Project Number: Quantifying flow habitat biota relationships in riverine ecosystems, Cooperative Research Centre for Freshwater Ecology Project A240.

MDFRC item.

30 pages. Year 1 synthesis report of 2 part report (see Part 2: Quantifying flow habitat biota relationships in riverine ecosystems: Successional processes in lowland river slackwaters: second year report).

River systems are diverse complex systems consisting of an array of patches that are largely formed through spatially and temporally variable geomorphic and hydrological processes. Flow is perhaps the overriding force in the structure and function of these patches. In this study we altered the nature of two major patch types in a lowland river (main channel flowing and slackwater) by directing flow into slackwater environments thereby creating a flowing patch and by directing flow away from an edge environment thereby creating a slackwater patch. We measured a range of biotic and abiotic variables in order to study the effects of altering flow characteristics within patches. Our results indicated that created flow and slackwater patches were equivalent to the natural habitats with respect to both their biotic and abiotic characteristics. Although there was no difference in the abiotic character and primary productivity of the flowing and slackwater patches, distinct biotic communities existed in these patch types. Microinvertebrate, fish and shrimp abundance was greatest in the slackwater habitats, whereas macroinvertebrate abundance was greatest in the flowing patch. Thus, the hydraulic nature of a patch determined the biotic communities of the patch. These distinct biotic communities may lead to a distinct food web structure in the two patch types and we present a conceptual model of a riverine flow-mediated food web. In addition, our results support the dynamic hierarchical patch model of organisation in river systems. Together, these models provide a valuable means of investigating patterns and process within a river system and highlight the need to maintain or reinstate the natural flow regime to ensure the spatial and temporal variability of patches for riverine health.