Do stream macroinvertebrates use instream refugia in response to severe short‐term flow reduction in New Zealand streams?

Abstract

1. Demand for water is increasing and water managers need to know how much they can remove from a stream before there are significant detrimental effects on its biological integrity. Flow reduction alters a number of habitat variables known to be important to aquatic invertebrates such as depth, velocity, temperature and fine sediment accumulation. Some taxa may attempt to use instream refugia to mitigate the effects of flow reduction. 2. We experimentally manipulated flows by constructing weirs and diversions in three small New Zealand streams. Discharge was reduced by 88-96%. We tested the hypothesis that macroinvertebrates would use pools and the hyporheic zone as refugia during shortterm (1-month) periods of reduced flow. 3. We sampled hyporheic invertebrates with colonization chambers and pool invertebrates with kick nets within a before-after, control-impact (BACI) experimental design. A suite of physicochemical parameters was measured concurrently including surface and hyporheic temperatures. 4. Flow reduction significantly decreased velocity (60-69%) in all streams. Depth (18-61%) and wetted width (24-31%) tended to decrease but these changes were not always significant. Sediment cover increased the most in farmland streams (10-80%). Apart from decreasing temperature range (18-26%), flow reduction had little impact on the surface water temperatures. 5. Flow reduction had no impact on the abundance of common pool macroinvertebrates or on the abundance, vertical distribution or community composition of hyporheic macroinvertebrates. 6. Our results suggest that aquatic macroinvertebrates are resistant to short-term, severe flow reduction as long as some water remains.

Is the hyporheic zone a refugium for aquatic macroinvertebrates during severe low flow conditions?

“…It is clear that the responses of macroinvertebrates within the benthic and hyporheic zones were not the same, demonstrating that care should be used when making inferences about hyporheic communities based on benthic sampling programmes. There is clearly a pressing need for further research which considers benthic and hyporheic communities simultaneously (James et al 2008, Stubbington et al 2009b) over both the medium and long term so that a greater understanding of the interactions across this dynamic ecotone can be obtained.…”

“…The different patterns recorded in benthic and hyporheic environments probably refl ect the magnitude of change recorded in these adjacent habitats. The marked reduction in water levels and exposure of parts of the riverbed at historically intermittent sites lead to signifi cant reductions in available habitat and the changes recorded within the benthic community abundance and taxa richness (James et al 2008). Even though the hyporheic zone was not dewatered or desiccated at any stage during the study, the response of the macroinvertebrate community signifi cantly differed between perennial and intermittent sites.…”

“…In perennial streams and those where climates are more temperate, and groundwater contribution is more reliable, presumably providing greater hyporheic (and benthic) stability, there is limited evidence of utilisation of the hyporheic zone as a refugium by the benthic fauna due to a reduction in river discharge (Delucchi 1989, del Rosario & Resh 2000, James et al 2008. The trigger for the proportion of benthos (particularly Gammarus pulex) within the hyporheic zone of the Little Stour to increase coincided with elevated air and water temperatures and associated parameters rather that a reduction in stream discharge alone and clearly warrants further detailed investigation.…”

“…Some studies have reported the occurrence of benthic and obligate hypogean fauna within the hyporheic zone during periods of river bed drying and fl ow cessation in naturally intermittent streams (Griffi th & Perry 1993, Clinton et al 1996, Hose et al 2005, Fenoglio et al 2006) whereas other research on intermittent systems has reported little or no use of the hyporheic zone by benthic fauna (Delucchi 1989, Smock et al 1994. In contrast, limited data exists for refugial responses to drought events in temperate perennial streams (Lake 2007, Wood & Armitage 2004, and very few studies have simultaneously considered benthic and hyporheic macroinvertebrate community response to severe low fl ows (exceptions being James et al 2008, Stubbington et al 2009b.…”

Extreme Climatic Events Alter Aquatic Food Webs

“…Experiments have been advocated as useful tools to explore the impact of unpredictable extreme events in natural systems (Jentsch et al, 2007), but research on drought and low flows in streams has tended to be phenomenological (but see, e.g. Dewson et al, 2007b;Walters and Post, 2011) and based on field surveys that are often confounded by environmental gradients or which lack the pre-impact data necessary to demonstrate causation (James et al, 2008). In the present study, we simulated hydrologic drought in a series of stream mesocosms over 2 years to capture intra-and intergenerational responses to habitat loss caused by periodic dewatering of benthic habitat (see Ledger et al, 2008Ledger et al, , 2011Ledger et al, , 2012Ledger et al, , 2013.…”