Dagmar Kappel Andersen

Headwater streams in the EU Water Framework Directive: Evidence-based decision support to select streams for river basin management plans

Headwater streams are important contributors to aquatic biodiversity and may counteract negative impacts of anthropogenic stress on downstream reaches. In Denmark, the first river basin management plan (RBMP) included streams of all size categories, most being <2.5m wide (headwater streams). Currently, however, it is intensely debated whether the small size and low slopes, typical of Danish streams, in combination with degraded habitat conditions obstruct their ability to fulfill the ecological quality objectives required by the EU Water Framework Directive (WFD). The purpose of this study was to provide an analytically based framework for guiding the selection of headwater streams for RBMP. Specifically, the following hypotheses were addressed: i) stream slope, width, planform, and general physical habitat quality can act as criteria for selecting streams for the next generation of RBMPs, and ii) probability-based thresholds for reaching good ecological status can be established for some or all of these criteria, thus creating a sound, scientifically based, and clear selection process. The hypotheses were tested using monitoring data on Danish streams from the period 2004-2015. Significant linear relationships were obtained between the ecological quality ratio assessed by applying the Danish Stream Fauna Index (DSFIEQR) and stream slope, width, sinuosity, and DHI. The obtained models were used to produce pressure-response curves describing the probability of achieving good ecological status along gradients in these parameters. Next, threshold values for slope, width, sinuosity, and DHI were identified for selected probabilities of achieving minimum good ecological status. The obtained results can support managers and policy makers in prioritizing headwater streams for the 3rd RBMP. The approach applied is broadly applicable and can, for instance, help prioritization of restoration and conservation efforts in different types of ecosystems where the biota can be significantly linked to separate and quantifiable environmental characteristics.

A new paradigm for biomonitoring – An example building on the Danish Stream Plant Index

Despite intensive efforts for more than a decade to develop Water Framework-compliant assessment systems, shortcomings continue to appear. In particular, the lack of reference conditions has hindered the development of assessment systems capturing the heart of the WFD – that ecological status should be set as the deviation from the natural, undisturbed condition. Recently, the Danish Stream Plant Index (DSPI) was developed. This system contrasts existing systems in that it builds on an expert interpretation of the normative definitions of ecological status classes in the WFD without taking pressure-impact relationships into account. Here, we substantiate the approach taken in the development of DSPI and examine if the DSPI class decreases with increasing level of anthropogenic stress and, additionally, if the deviation from the natural undisturbed condition increases with decreasing DSPI class sensu WFD using trait composition of plant assemblages from Danish streams around year 1900 as a reference. We furthermore examine the trait composition of the vegetation in sites classified into different DSPI status classes to explore if predictable patterns exist that can be used to identify the ultimate cause(s) of failure to meet ecological goals and help guide the selection of appropriate mitigation measures. We observed that DSPI declined with several parameters indicative of environmental stress in Danish streams and, furthermore, that the deviation from the natural undisturbed condition regarding the trait composition of plant communities declined with increasing DSPI, implying that the trait composition of plant communities in the high DSPI status class was most similar to those occurring in Danish streams around year 1900. We also found that trait characteristics capable of disentangling important stressors in Danish streams varied consistently among sites classified into different DSPI classes. Based on our findings, we call for new thinking. We suggest that more effort should be directed at describing reference conditions and interpreting the normative definitions of good, moderate, poor and bad instead of focusing solely on developing assessment systems using pressure-impact frameworks. We find this particularly important with respect to streams since these are seldom impacted by only a single stressor. This article is protected by copyright. All rights reserved.

N- and P-addition inhibits growth of rich fen bryophytes

A greenhouse experiment was set up to investigate if infrequently and frequently occurring species respond differently to simulated habitat changes. Two frequently occurring (Bryum pseudotriquetrum and Calliergonella cuspidata) and two infrequently occurring (Hamatocaulis vernicosus and Paludella squarrosa) rich fen bryophytes were grown in mixed culture and subjected to rainwater or groundwater and three levels of N, ammonium nitrate (0, 1 and 3 mg N L–1) and P, potassium phosphate (0, 0.05 and 0.1 mg P/L). All species responded negatively to higher N-levels and three of the four species responded negatively to rainwater and higher P-levels. C. cuspidata had highest relative growth rate (RGR) in all treatments, and the infrequently occurring species had lower RGR and were more negatively affected by high levels of N than the frequently occurring species. A negative effect of rainwater seemed to be caused by higher background levels of N in rainwater compared to groundwater. We found a negative effect of high initial bryophyte density in three of the four species indicating density-dependent inhibition between species. We suggest that maintenance of oligotrophic conditions by recharge of nutrient-poor groundwater is vital for conservation of infrequently as well as frequently occurring rich fen bryophytes.

Structural and functional characteristics of buffer strip vegetation in an agricultural landscape – high potential for nutrient removal but low potential for plant biodiversity

Vegetated buffer strips constitute a transition zone between terrestrial and aquatic ecosystems and provide several ecosystem services. Buffer strips are often applied as a mitigation measure against diffuse pollution in agricultural areas, primarily because they may retain nutrients and in this way help protect the aquatic environment. Additionally, they can improve biodiversity in an otherwise homogenous landscape and may therefore have a value in their own right. In the present study, we characterized the structural and functional features of the vegetation in Danish buffer strips using a nationwide dataset to explore: i) their floristic quality in terms of species diversity and conservation value and ii) based on their functional characteristics, their potential to retain nutrients. Moreover, we analyzed how the structural and functional characteristics varied along gradients in the environmental features of the catchment. We found that the floristic quality of the buffer vegetation was generally low, exhibiting an average of only 3.3% of the number of species of conservation interest. Instead, Danish buffer strips were dominated by widespread and productive species that are tolerant of anthropogenic impacts in the catchment. The abundance of highly productive plant species was positively related to high intensity land use, whereas the abundance of stress-tolerant plant species was positively related to low intensity land use. The high productivity of the buffer strips implies a large bio-storage potential, and these areas might therefore offer an opportunity to remove nutrients by harvesting the plant biomass. We discuss how Danish buffer strips could be exploited via appropriate management (e.g. harvesting) to maximize nutrient retention and at the same time improve floristic quality.