Hydrological controls of DOC export from Nordic headwater catchments.

<p>Nordic surface waters are currently much browner than during the 1980s due to drivers related to decreased acid deposition, and increased precipitation. While upward trends in concentration of DOC have been well documented, positive trends in the annual export of DOC are not as widespread. The variation in seasonality of DOC export may mask long-term trends in annual export. A large dataset of 30 natural headwater catchments from Finland, Norway, and Sweden contains more than 20 years of discharge and DOC records. We will use these data to better quantify the trends of DOC export and their relationships to seasonality and the effects of climatic changes seen over the last few decades, such as diminished snowpack, less distinct snowmelt events and increases in autumn precipitation. We will investigate both the seasonal and annual relationships between DOC concentration and discharge (C-Q) and test if they relate to time and catchment characteristics such as size, latitude, and landcover.</p><p>We explore 3 hypotheses in this data set. First, spring DOC export is decreased due to less distinct snowmelt and runoff events while autumn export of DOC is increased as a consequence of more autumn runoff. Second, we propose that catchments with a longer or more distinct snow cover period are more sensitive than catchments at lower elevation or latitude due to the length of inactivity caused by low temperatures and a more defined snowmelt runoff event. Third, we hypothesize the negative C-Q relationship in winter and spring is likely due to source limitation and dilution while hydrologic controls in summer and autumn are associated with positive C-Q relationships.</p><p>Climate change is promoting enhanced export of DOC from soils towards surface waters, leading to more carbon processed and transported along the aquatic continuum from headwaters to coast. This data set gives us an opportunity to look at a diverse set of headwater catchments in the Nordic region, an area disproportionally affected by climate change, to clarify the hydrologic components and how this will affect overall carbon transport. </p>

Modeling the Impact of Riparian Hollows on River Corridor Nitrogen Exports

Recent studies in snowmelt-dominated catchments have documented changes in nitrogen (N) retention over time, such as declines in watershed exports of N, though there is a limited understanding of the controlling processes driving these trends. Working in the mountainous headwater East River Colorado watershed, we explored the effects of riparian hollows as N-cycling hotspots and as important small-scale controls on observed watershed trends. Using a modeling-based approach informed by remote sensing and in situ observations, we simulated the N-retention capacity of riparian hollows with seasonal and yearly hydrobiogeochemical perturbations imposed as drivers. We then implemented a scaling approach to quantify the relative contribution of riparian hollows to the total river corridor N budget. We found that riparian hollows primarily serve as N sinks, with N-transformation rates significantly limited by periods of enhanced groundwater upwelling and promoted at the onset of rainfall events. Given these observed hydrologic controls, we expect that the nitrate (NO3-) sink capacity of riparian hollows will increase in magnitude with future climatic perturbations, specifically the shift to more frequent rainfall events and fewer snowmelt events, as projected for many mountainous headwater catchments. Our current estimates suggest that while riparian hollows provision ~5–20% of NO3- to the river network, they functionally act as inhibitors to upland NO3- reaching the stream. Our work linking transient hydrological conditions to numerical biogeochemical simulations is an important step in assessing N-retaining features relative to the watershed N budget and better understanding the role of small-scale features within watersheds.

A Need for Standardized Reporting: A Scoping Review of Bioretention Research 2000–2019

Bioretention cells are a type of low-impact development technology that, over the past two decades, have become a critical component of urban stormwater management. Research into bioretention has since proliferated, with disparate aims, intents and metrics used to assess the “performance” of bioretention cells. We conducted a comprehensive, systematic scoping review to answer the question of “How is the field performance of bioretention assessed in the literature?”, with the aim of understanding (1) how is the performance of bioretention defined in the literature? (2) what metrics are used to assess actual and theoretical performance? A review of 320 studies (mostly peer reviewed articles) found that performance was defined in terms of hydrologic controls, while investigations into water quality pathways and mechanisms of contaminant transport and fate and the role of vegetation were lacking; additionally, long term field and continuous modelling studies were limited. Bioretention field research was primarily conducted by a small number of institutions (26 institutions were responsible for 50% of the research) located mainly in high income countries, particularly Australia and the United States. We recommend that the research community (I) provide all original data when reporting results, (II) prioritize investigating the processes that determine bioretention performance and (III) standardize the collection, analysis and reporting of results. This dissemination of information will ensure that gaps in bioretention knowledge can be found and allow for improvements to the performance of bioretention cells around the world.

Influence of Desert Springs on Habitat of Endangered Zuni Bluehead Sucker (Catostomus discobolus yarrowi)

ABSTRACT Located on the southeastern part of the Colorado Plateau, the Zuni Mountains are home to the endangered Zuni Bluehead Sucker (ZBS) (Catostomus discobolus yarrowi). A 4-year study was conducted on a low-flow (<80 cm3/s) hillslope spring and intermittent stream, that are home to one of the three remaining ZBS populations. Seasonal measurements of physical and hydrochemical parameters were used to estimate the contribution of groundwater to the stream and to identify geologic and hydrologic controls for the spring discharge. Seasonal concentrations and standard deviations (s) of Mg2+ were used to determine that the spring water (5.6 mg/L; s = 0.4) and surface water up-gradient from the spring input (10.7 mg/L; s = 11.2) is from different sources. Surface water down-gradient from the spring input maintain ZBS populations and is a mixture of spring water and up-gradient surface water. Mass solution mixing was used to determine spring water contributes up to 99 percent of the down-gradient water during drier seasons. Isotopes (δD, δ18O, 3H) indicate that the spring water has been recharged primarily from snowmelt within the last 70 years, while up-gradient surface water is seasonal runoff from rain and snowmelt. Continuous monitoring of dissolved oxygen (DO) mean concentrations (up-gradient = 1.6 mg/L and down-gradient = 5.7 mg/L) indicated that surface water up-gradient from the spring input are anoxic and unable to support ZBS. Surface water down-gradient from the spring input maintain appropriate DO concentrations due to perennially discharging spring waters re-aerating downstream habitats.