| 1. |
- Lupon, Anna
(författare)
-
The influence of Mediterranean riparian forests on stream nitrogen dynamics: a review from a catchment perspective
- 2017
-
Ingår i: Limnetica. - : Asociacion Iberica de Limnologia. - 0213-8409 .- 1989-1806. ; 36, s. 507-523
-
Tidskriftsartikel (refereegranskat)abstract
- Riparian zones are considered natural filters of nitrogen (N) within catchments because they can substantially diminish the exports of N from terrestrial to aquatic ecosystems. However, understanding the influence of riparian zones on regulating N exports at the catchment scale still remains a big challenge in ecology, mainly because upscaling plot scale results is difficult, as it is disentangling the effects of riparian, upland, and in-stream processes on stream water chemistry. In this review, we summarize previous studies examining key hydrological and biogeochemical processes by which Mediterranean riparian zones regulate catchment water and N exports. We focus on Mediterranean regions because they experience a marked climatic seasonality that facilitates disentangling the close link between climate, riparian hydrology, and stream N exports. We show that Mediterranean riparian soils can be hot spots of N mineralization and nitrification within catchments given their relatively moist conditions and large stocks of N-rich leaf litter. Extremely large nitrification rates can occur during short-time periods (i.e. hot moments) and lead to increases in stream N loads, suggesting that riparian soils can be a potential source of N to adjacent aquatic systems. Moreover, riparian trees can contribute to decrease riparian groundwater level during the vegetative period, and promote reverse fluxes from the stream to the riparian zone. During periods of high hydrological retention, stream water exports to downstream ecosystem decrease, while stream water chemistry is mostly determined by in-stream processes. Riparian tree phenology can also affect catchment N exports by shaping the temporal pattern of both light and litter inputs into the stream. In spring, light enhances in-stream photoautotrophic N uptake before riparian leaf-out, while riparian leaf litter inputs promote in-stream N mineralization in summer and fall. Finally, we illustrate that the impact of Mediterranean riparian zones on stream hydrology and biogeochemistry increases along the stream continuum, and can ultimately influence catchment N exports to downstream ecosystems. Overall, findings gathered in this review question the well-established idea that riparian zones are efficient N buffers, at least for Mediterranean regions, and stress that an integrated view of upland, riparian, and stream ecosystems is essential for advancing our understanding of catchment hydrology and biogeochemistry.
|
|
| 2. |
- Pastor, Ada, et al.
(författare)
-
Local and regional drivers of headwater streams metabolism : insights from the first AIL collaborative project
- 2017
-
Ingår i: LIMNETICA. - : Asociacion Iberica de Limnologia. - 0213-8409 .- 1989-1806. ; 36:1, s. 67-85
-
Tidskriftsartikel (refereegranskat)abstract
- Streams play a key role in the global biogeochemical cycles, processing material from adjacent terrestrial systems and transporting it downstream. However, the drivers of stream metabolism, especially those acting at broad spatial scales, are still not well understood. Moreover, stream metabolism can be affected by hydrological changes associated with seasonality, and thus, assessing the temporality of metabolic rates is a key question to understand stream function. This study aims to analyse the geographical and temporal patterns in stream metabolism and to identify the main drivers regulating the whole ecosystem metabolic rates at local and regional scales. Using a coordinated distributed experiment, we studied ten headwaters streams located across five European ecoregions during summer and fall 2014. We characterized the magnitude and variability of gross primary production (GPP) and ecosystem respiration (ER) with the open-channel method. Moreover, we examined several climatic, geographical, hydrological, morphological, and physicochemical variables that can potentially control stream metabolic rates. Daily rates of stream metabolism varied considerately across streams, with GPP and ER ranging from 0.06 to 4.33 g O-2 m(-2) d(-1) and from 0.72 to 14.20 g O-2 m(-2) d(-1), respectively. All streams were highly heterotrophic (P/R < 1), except the southernmost one. We found that the drier climates tended to have the highest GPP, while humid regions presented the highest ER. Between the sampling periods no statistical differences were found. Partial-least squares models (PLS) explained similar to 80% of the variance in GPP and ER rates across headwater streams and included both local and regional variables. Rates of GPP varied primarily in response to the local variables, such as streambed substrate and stream water temperature. In contrast, regional variables, such as the mean annual temperature or the land use of the catchment, had more relevance to explain ER. Overall, our results highlight that stream metabolism depends on both local and regional drivers and show the positive experience of a young network of researchers to assess scientific challenges across large-scale geographic areas.
|
|
