Dissolved organic matter composition in a fragmented Mediterranean fluvial system under severe drought conditions

Vázquez, Eusebi; Amalfitano, Stefano; Fazi, Stefano; Butturini, Andrea

doi:10.1007/s10533-010-9421-x

Cited by 84 publications

(65 citation statements)

References 51 publications

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“…Hydrologic and biogeochemical differences between pools can contribute to heterogeneity in habitat quantity and quality during dry periods (Fellman et al 2011, Vazquez et al 2011. For example, drying-induced fragmentation concentrates organic matter (Towns 1985, Stanley et al 1997, Caruso 2002, which, when combined with high microbial respiration and low air-water gas exchange rates, can subsequently deplete dissolved oxygen (DO; Acuña et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Abiotic habitat thresholds for salmonid over‐summer survival in intermittent streams

2017

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Abstract. Intermittent streams lose surface flow during part of the year but can provide important habitat for imperiled fishes in residual pools. However, extended intermittency can drive high mortality as pool contraction decreases pool quality, and some pools dry completely. We evaluated the influence of a suite of abiotic habitat characteristics on the over-summer survival of two imperiled salmonid fishes (coho salmon Oncorhynchus kisutch; steelhead trout Oncorhynchus mykiss) at four study sites on two tributaries of Salmon Creek (Sonoma County, California, USA) from 2012 to 2014, during deepening drought conditions. Study sites spanned an intermittency gradient from continuous flow to near-dry conditions, and included alluvial and bedrock stream reaches. We estimated over-summer survival at the pool scale from fish presenceabsence data based on paired early-late summer snorkel surveys. We measured pool dimensions and water quality parameters monthly (more frequently during summer dry down) and, in 2013 and 2014, recorded water quality with continuous loggers in selected pools. We performed: (1) logistic regression in a generalized linear modeling framework to identify factors limiting over-summer survival and (2) classification trees using the random forests ensemble learning method to identify abiotic thresholds for sustaining salmonids. Results suggested that different factors governed mortality of the two species. Coho salmon, which tended to survive in large, deep pools, were limited by minimum dissolved oxygen (DO) concentrations. In contrast, steelhead trout, which tended to survive in pools with large surface area, were sensitive to pool geometry and temperature. Both species persisted for weeks in large pools with low DO levels, including in pools where at least part of the water column reached sublethal or lethal levels. Our results suggest that shallow, lateral hyporheic flow may be important for maintaining DO and temperatures suitable for sustaining salmonids in isolated pools, whereas groundwater discharge originating from deeper flow paths may generate low-DO conditions that inhibit salmonid persistence. Geomorphically complex watersheds with a variety of pool geometries and high rates of lateral hyporheic exchange are those most likely to serve as "sanctuary reaches" for imperiled Pacific salmonid populations in semi-arid regions in the context of a changing climate.

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Section: Introductionmentioning

confidence: 99%

Abiotic habitat thresholds for salmonid over‐summer survival in intermittent streams

2017

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“…Overall, the loss of NO 3 was compensated by the increase in NH 4 , and in-stream processing did not alter the relative availability of dissolved organic and inorganic N forms. Previous studies in this stream showed that during baseflow or fragmented flow conditions, a high proportion of TDN is available as DON (Bernal et al 2005;Vazquez et al 2011). Interestingly, this balance was interrupted by a sharp increase in DON concentration at the end of the fragmentation phase, probably due to an abrupt microbial biofilm cell lysis or DON exudation under stress conditions (e.g.…”

Section: Temporal Variation In Nutrient Concentrationsmentioning

confidence: 91%

“…During stream expansion after rewetting, high concentrations of nitrogen (N) and phosphorus (P) originate from groundwater inputs and from leaching of accumulated organic material (Tzoraki et al 2007;Obermann et al 2009;Skoulikidis and Amaxidis 2009). The effect of flow intermittency on the fate of organic N and P is less well understood, although an increase in the concentration of dissolved organic N (DON) during stream fragmentation and expansion has been attributed to high microbial production and leaching, respectively (Vazquez et al 2007;Skoulikidis and Amaxidis 2009;Ylla et al 2010;Vazquez et al 2011). Knowledge on the dynamics of organic P is virtually restricted to rewetting periods when the concentration of dissolved organic P (DOP) tends to increase (Tzoraki et al 2007;Skoulikidis and Amaxidis 2009).…”

Section: Introductionmentioning

confidence: 99%

Contraction, fragmentation and expansion dynamics determine nutrient availability in a Mediterranean forest stream

Schiller

Acuña

Graeber³

et al. 2011

Aquat Sci

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Temporary streams are a dominant surface water type in the Mediterranean region. As a consequence of their hydrologic regime, these ecosystems contract and fragment as they dry, and expand after rewetting. Global change leads to a rapid increase in the extent of temporary streams, and more and more permanent streams are turning temporary. Consequently, there is an urgent need to better understand the effects of flow intermittency on the biogeochemistry and ecology of stream ecosystems. Our aim was to investigate how stream nutrient availability varied in relation to ecosystem contraction, fragmentation and expansion due to hydrologic drying and rewetting. We quantified the temporal and spatial changes in dissolved nitrogen (N) and phosphorus (P) concentrations along a reach of a temporary Mediterranean forest stream during an entire contraction-fragmentation-expansion hydrologic cycle. We observed marked temporal changes in N and P concentrations, in the proportion of organic and inorganic forms as well as in stoichiometric ratios, reflecting shifts in the relative importance of in-stream nutrient processing and external nutrient sources. In addition, the spatial heterogeneity of N and P concentrations and their ratios increased substantially with ecosystem fragmentation, reflecting the high relevance of in-stream processes when advective transport was lost. Overall, changes were more pronounced for N than for P. This study emphasizes the significance of flow intermittency in regulating stream nutrient availability and its implications for temporary stream management. Moreover, our results point to potential biogeochemical responses of these ecosystems in more temperate regions under future water scarcity scenarios.

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“…Following the rationale of Yu et al (2002) and our observations of increasing protein-like moieties and decreasing molecular weight of DOM with soil depth, we hypothesize that the protein-like fluorescence we observed in groundwater are likely free forms of the proteins. Vazquez et al (2007Vazquez et al ( , 2010 also concluded that proteinaceous DOM associated with groundwater was of low molecular weight.…”

Section: Changes In Dom Concentrations and Quality Across Watershed Smentioning

confidence: 99%

Dissolved organic matter (DOM) concentration and quality in a forested mid-Atlantic watershed, USA

et al. 2011

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Understanding the quantity and quality of dissolved organic matter (DOM) in potential watershed sources is critical for explaining and quantifying the exports of DOM in stream runoff. Here, we examined the concentration and quality of DOM for ten watershed sources in a 12 ha forested catchment over a two-year period. DOM composition was evaluated for: throughfall, litter leachate, soil water (zero and tension), shallow and deep groundwater, stream water, hyporheic zone, and groundwater seeps. DOM quality was measured using a suite of optical indices including UV-visible absorbance and PARAFAC modeling of fluorescence excitationemission matrices (EEMs). DOM concentrations and quality displayed a pronounced trend across watershed sources. Surficial watershed sources had higher DOM concentrations and more humic-like DOM with higher molecular weight whereas deeper groundwater sources were rich in % protein-like fluorescence. The greater % contribution of proteinlike fluorescence in groundwater suggested that a larger fraction of groundwater DOM may be bioavailable. DOM for wetland groundwater was more aromatic and humic-like than that at the well-drained riparian location. Principal component analyses (PCA) revealed that the differences in surficial watershed compartments were dictated by humic-like components while groundwater sources separated out by % protein-like fluorescence. Observations from optical indices did not provide any conclusive evidence for preferential association of dissolved organic carbon (DOC) or dissolved organic nitrogen (DON) with any particular DOM quality pools.

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Dissolved organic matter composition in a fragmented Mediterranean fluvial system under severe drought conditions

Cited by 84 publications

References 51 publications

Abiotic habitat thresholds for salmonid over‐summer survival in intermittent streams

Abiotic habitat thresholds for salmonid over‐summer survival in intermittent streams

Contraction, fragmentation and expansion dynamics determine nutrient availability in a Mediterranean forest stream

Dissolved organic matter (DOM) concentration and quality in a forested mid-Atlantic watershed, USA

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