Influence of contrasting riparian forest cover on stream temperature dynamics in salmonid spawning and nursery streams

Abstract

In this paper, we investigated the influence of contrasting riparian forest types on upland stream temperatures and the links between thermal regime and standard indices of forest cover. Stream temperature was measured for two hydrological years at multiple sites along two tributaries of the River Dee, Scotland. Riparian cover in the upper reaches of both streams was dominated by Calluna moorland while the lower sections comprised either dense alluvial broadleaved forest (Girnock Burn) or native Scots Pine stands (Tanar). The Point‐Centered‐Quarter Method was used to quantify stem density (SD) and tree coverage (TC) as an indicator of channel shading comprising either dense alluvial broadleaved forest (Girnock Burn) or native Scots Pine stands (Tanar). The greatest reductions in maximum temperature (4 °C) and diel amplitude (6·6°C) were observed where TC and SD were greatest in areas of relatively dense broadleaved riparian cover. Analysis of the relationship between forest characteristics and temperature summary statistics revealed that SD and TC were significant predictors of mean and maximum temperatures, as well as daily temperature ranges for both rivers during the summer. The relationship between summer thermal indices and indicators of channel shading (SD or TC) was independent of forest type. However, as SD and TC were greater in the deciduous reaches of Glen Girnock than the mature Scots pine reaches of Glen Tanar, maximum reductions in stream temperature were greater in Glen Girnock. Given that maximum temperatures were strongly influenced by measures of shading, it suggested that riparian planting may offer a suitable mitigation against high temperatures under climate change. Copyright © 2012 John Wiley & Sons, Ltd.

Can spatial statistical river temperature models be transferred between catchments?

“…For example, the approximately 20 % variance explained by UCA in the Spey and Dee models is consistent with the 18-25 % of T w variability explained by discharge in Arora et al (2016). Smaller-scale variability tends to reflect drivers such as water residence time (and heat advection), water sources (Brown et al, 2006;, channel incision, gradient (Jackson et al, 2017b) and land use (Imholt et al, 2013) which are harder to accurately characterise from spatial datasets. In the absence of accurate local-scale characterisation of landscape controls, smallerscale spatial variability is modelled by the RNS.…”

“…In common with similar modelling studies (Hrachowitz et al, 2010;Imholt et al, 2011;Jackson et al, 2017b;Ruesch et al, 2012), no interactions were considered between covariates due to data constraints.…”

“…UCA (which was in all the models) is a proxy for discharge, water volume and thermal capacity (Chang and Psaris, 2013;Hannah et al, 2008). Higher UCAs are generally associated with larger water volumes which have a greater thermal capacity, taking longer to warm but also retaining heat for longer (Chang and Psaris, 2013;Imholt et al, 2011). Elevation reflects adiabatic lapse rates which reduce temperatures with increasing altitude (Hrachowitz et al, 2010;Jackson et al, 2017b).…”

“…Large-scale models are required to provide information at the spatial scales appropriate to management decisions, i.e. catchment (Chang and Psaris, 2013;Hrachowitz et al, 2010;Imholt et al, 2011Imholt et al, , 2013Jackson et al, 2017b;Steel et al, 2016), regional (Hill et al, 2013;Isaak et al, 2012;Ruesch et al, 2012) and national scales.…”

Past and present land use influences on tropical riparian zones: an isotopic assessment with implications for riparian forest width determination

“…When these streamside ecosystems are under forest cover these areas are considered to be important due to a series of reasons: (i) protection of stream banks against erosion and bank sliding (Abernethy & Rutherford 2000); (ii) reduction of erosion and input of soil particles into the stream (Lowrance et al 1986, Verstraeten et al 2006, Pires et al 2009); (iii) shading and reduction of the water temperature (important for fish reproduction) (Imholt et al 2013); (iv) riparian forests provide nutrients and carbon to aquatic communities (Lowrance et al 1985); and they might also increase the input of coarse woody debris to the stream channel, which is important in creating habitat diversity within the stream environment (De Paula et al 2011). These attributes of riparian forests are especially important in watersheds dominated by upland agricultural fields, where soil disturbance by cultivation and use of fertilizers and agrochemicals are frequent.…”