Dynamic processes of hyporheic exchange and temperature distribution in the riparian zone in response to dam-induced water fluctuations

P.J.B.); J.Drummond@bham.ac.uk (J.D.D.); D.M.HANNAH@bham.ac.uk (D.M.H.); S.Krause@bham.ac.uk (S.K.); a.m.milner@bham.ac.uk (A.M.)Abstract: Time-variable discharge is known to control both transport and transformation of solutes in the river corridor. Still, few studies consider the interactions of transport and transformation together. Here, we consider how diurnal discharge fluctuations in an intermittent, headwater stream control reach-scale solute transport and transformation as measured with conservative and reactive tracers during a period of no precipitation. One common conceptual model is that extended contact times with hyporheic zones during low discharge conditions allows for increased transformation of reactive solutes. Instead, we found tracer timescales within the reach were related to discharge, described by a single discharge-variable StorAge Selection function. We found that Resazurin to Resorufin (Raz-to-Rru) transformation is static in time, and apparent differences in reactive tracer were due to interactions with different ages of storage, not with time-variable reactivity. Overall we found reactivity was highest in youngest storage locations, with minimal Raz-to-Rru conversion in waters older than about 20 h of storage in our study reach. Therefore, not all storage in the study reach has the same potential biogeochemical function and increasing residence time of solute storage does not necessarily increase reaction potential of that solute, contrary to prevailing expectations.

Section: Introductionmentioning

confidence: 99%

Solute Transport and Transformation in an Intermittent, Headwater Mountain Stream with Diurnal Discharge Fluctuations

Ward

Kurz

Schmadel

et al. 2019

“…The field site is located in the riparian zone (29 • 24' N, 119 • 21' E) downstream of the Xin'an River Dam, Jiande, China (see [15] for details). The river water level at the site has been often affected by the upstream reservoir discharge for years, with the amplitude up to 1 m. Three water-level monitoring wells were arranged along the cross section of the riparian zone.…”

Section: Study Sitementioning

confidence: 99%

Feasible Ways Promoting Nitrate Removal in Riparian Zone Downstream of a Regulated River

Liu

Zhu

et al. 2020

Self Cite

Set in the downstream riparian zone of Xin’an River Dam, this paper established a 2D transversal coupling flow and solute transport and reaction model by verification within situ groundwater level and temperature. The denitrifying methods and principles in the riparian zone from the perspective of hyporheic exchange were explored, which provided a basis for the engineering techniques for river ecological restoration. Our studies have shown that under the condition of water level fluctuation, a biological method such as adding denitrifying bacteria biomass to a fixed degree (the same below) can greatly increase the denitrifying rate (1.52 g/d) in the riparian zone; chemical methods such as adding organic carbon into the surface water or groundwater can increase the total riparian nitrate removal (8.00–8.18 g) and its efficiency (19.5–20.0%) to a great extent; hydrogeological methods such as silt cleaning of the aquifer surface or local pumping around the contaminated area can increase the total riparian nitrate removal (1.06–14.8 g) to some extent, but correspondingly reduce the denitrifying efficiency (0.95–1.4%); physical methods such as designing the bank form into gentle slope or concave shape can slightly increase the total riparian nitrate removal (0.22–0.52 g) and correspondingly improve the denitrifying efficiency (0.25–0.85%). At the application level of river ecological restoration, integrated adopting the above methods can make the riparian denitrifying effect “fast and good”.

“…Several factors can potentially alter the hydrological connectivity of the subsurface habitats from surface waters as well as from the underlying aquifer [41,42], critically influencing hyporheic invertebrate communities [43][44][45]. Among them, important ones are alteration of streamflow dynamics, changes in streambed and river banks structure and morphology, and reduction of streambed sediments heterogeneity (i.e., colmation or clogging [46]), mainly arising from the presence of dams [42,[47][48][49], barriers, water derivation works, and groundwater overexploitation [21] (HHYC = altered habitat due to hydrological changes [50]).…”

Section: Section 2: Hydrological-hydromorphological Riskmentioning

confidence: 99%

AQUALIFE Software: A New Tool for a Standardized Ecological Assessment of Groundwater Dependent Ecosystems

Strona

Fattorini

Fiasca

et al. 2019

We introduce a suite of software tools aimed at investigating multiple bio-ecological facets of aquatic Groundwater Dependent Ecosystems (GDEs). The suite focuses on: (1) threats posed by pollutants to GDE invertebrates (Ecological Risk, ER); (2) threats posed by hydrological and hydromorphological alterations on the subsurface zone of lotic systems and groundwater-fed springs (Hydrological-Hydromorphological Risk, HHR); and (3) the conservation priority of GDE communities (Groundwater Biodiversity Concern index, GBC). The ER is assessed by comparing tolerance limits of invertebrate species to specific pollutants with the maximum observed concentration of the same pollutants at the target site(s). Comparison is based on an original, comprehensive dataset including the most updated information on tolerance to 116 pollutants for 474 freshwater invertebrate species. The HHR is assessed by accounting for the main direct and indirect effects on both the hyporheic zone of lotic systems and groundwater-fed springs, and by scoring each impact according to the potential effect on subsurface invertebrates. Finally, the GBC index is computed on the basis of the taxonomical composition of a target community, and allows the evaluation of its conservation priority in comparison to others.