Rivers – Relationship between nutrient retention metrics and habitat/local hydromorphology indicators

INHABIT project

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Home Themes & Results Nutrients (I2) Retention metrics and habitat descriptors relationship

Rivers – Relationship between nutrient retention metrics and habitat/local hydromorphology indicators

Nutrient retention in lotic environments results from hydrological, biological and chemical retention. Hydrological retention depends on hydromorphological features slowing water flow and increasing interactions among surface water, sediment and hyporheic zone. The higher the residence time, the higher is the chance nutrients availability for biotic communities.
With the aim of evaluating the interaction between capacity of nutrient retention and hydromorphological characteristics, calculated retention metrics have been related to a set of physical variables measured along the 100m experimental reach. In particular relations between retention metrics and hydrological/hydraulic parameters (discharge, flow velocity and water transient storage zones) and morphological parameters (average width and depth and flow and substrate type). Retention metrics have been also compared with some descriptive indices of local hydromorphological alteration and habitat, calculated from CARAVAGGIO method. Attention has been put to the analysis of nutrients retention processes in river reaches located downstream to specific morphological alterations (e.g. fords, bank reinforcements, culverts etc.)
Among the obtained results, most notable is the significant relation between uptake length (for both NH4 and PO4) and transient storage areas normalized against total river section (As/A). Retention efficiency increases with the increasing of transient storage areas since, as expected, the presence of these areas increases contact time between water and biologically active surfaces, such as sediments. As highlighted in the following graphs relations are statistically highly  significant for Sardinian streams (on the left) while for Piedmont sites (on the right) lesser significance is related to the lower amount of available data.



For what hydromorphological alterations is concerned, some heavily altered sites (showing high Habitat Modification Score) showed no orthophosphate removal. In other cases the presence of one or more culvert, such as for Baldu and Lorana sites, has presumably caused a decline in ammonium retention downstream the alteration.

Corr'è Pruna
Lorana Valle
HMS = 79
PO4 no retention
HMS = 43
PO4 no retention