Abstract:Although widely used in wetland hydrological studies, hydraulic conductivity (K) estimates from piezometer slug tests are often of questionable validity. Frequently, this is because insufficient attention is paid to the details of the test procedure. Further, in a potentially heterogeneous and anisotropic medium such as peat, the use of slug tests is prone to error. In this paper we address some of the methodological issues surrounding piezometer slug tests in peat. We compare slug test data with laboratory determinations of vertical and horizontal K obtained using a new method. Piezometers were installed at three depths in a floodplain fen peat in Norfolk, UK. Slug tests were initiated by both slug insertion and slug withdrawal, and repeat tests were conducted to examine the robustness of our K estimates. Most of the tests displayed departures from the log-linear model of Hvorslev, the form of departure being consistent with compressible soil behaviour. The results suggest that insertion tests gave similar results to those initiated by withdrawal. Repeat testing showed that withdrawal data, in particular, gave highly reproducible normalized responses that were independent of the initial head. Values for K estimated using the slug tests were in the range 1 ð 10 4 to 1Ð6 ð 10 3 cm s 1 , which is towards the upper end of the range reported for peats generally. Laboratory tests yielded similar values of K to those obtained from the slug tests. Although the laboratory tests showed that the peat was anisotropic, the K values generated by slug testing proved relatively good estimates of both vertical and horizontal K.

Phosphorus losses from land to water will be impacted by climate change and land management for food production, with detrimental impacts on aquatic ecosystems. Here we use a unique combination of methods to evaluate the impact of projected climate change on future phosphorus transfers, and to assess what scale of agricultural change would be needed to mitigate these transfers. We combine novel high-frequency phosphorus flux data from three representative catchments across the UK, a new high-spatial resolution climate model, uncertainty estimates from an ensemble of future climate simulations, two phosphorus transfer models of contrasting complexity and a simplified representation of the potential intensification of agriculture based on expert elicitation from land managers. We show that the effect of climate change on average winter phosphorus loads (predicted increase up to 30% by 2050s) will be limited only by large-scale agricultural changes (e.g., 20–80% reduction in phosphorus inputs).

10Eutrophication is a globally significant challenge facing aquatic ecosystems, associated with human 11 induced enrichment of these ecosystems with nitrogen (N) and phosphorus (P). However, the limited 12 availability of inherent labels for P and N has constrained understanding of the triggers for 13 eutrophication in natural ecosystems and appropriate targeting of management responses. This paper 14 proposes and evaluates a new multi-stable isotope framework that offers inherent labels to track 15 biogeochemical reactions governing both P and N in natural ecosystems. importance of abiotic and metabolic processes for the in-river fate of N and P are also explored 27 through the stable isotope framework. Microbial uptake of ammonium to meet metabolic demand for 28 N is suggested by substantial enrichment of δ 15 N NH4 (by 10.2‰ over a 100m reach) under summer 29 low flow conditions. Whilst the concentration of both nitrate and phosphate decreased substantially 30 along the same reach, the stable isotope composition of these ions did not vary significantly, 31indicating that concentration changes are likely driven by abiotic processes of dilution or sorption. 32The in-river stable isotope composition and the concentration of P and N were also largely constant 33 downstream of the waste water treatment works, indicating that effluent-derived nutrients were not 34 strongly coupled to metabolism along this in-river transect. Combined with in-situ and laboratory 35 hydrochemical data, we believe that a multi-stable isotope framework presents a powerful approach 36 for understanding and managing eutrophication in natural aquatic ecosystems. 37 38

Raised bogs are important ecohydrological systems in which there are strong two-way links between plant succession, litter and peat decay, and hydrological functioning. Using recently established protocols, we measured the hydraulic structure of a raised bog in West Wales. We tested two hypotheses: (i) that the hydraulic conductivity (K) of the peat shows depth dependency such that lower layers of peat are effectively impermeable, and (ii) that the K of the marginal peat of the bog dome is lower than that in central areas. From 107 piezometer measurements we found there was depth dependency of K but that lower peat layers were not poorly permeable or impermeable. We also found that the K of the peat on the margin of the bog dome was generally significantly lower than that in central areas. Our results suggest that, for some bogs at least, it is important to simulate water flow through deeper peats when simulating peatland development or growth. They also raise the intriguing possibility that the low K of marginal peat is important in maintaining wet conditions in central bog areas, allowing bogs to reach greater thicknesses than they would do in the absence of the low-K margin; an idea first proposed for blanket bogs by Lapen et al. (2005).

Abstract:Despite their common global occurrence, little work has been done on characterizing the hydraulic properties of root mats, particularly their hydraulic conductivity K. A common method for estimating K in the field is the piezometer slug test. In some root mat systems, the piezometer slug test may be the only technique, field or laboratory, that is able to provide reliable estimates of K. We installed 17 piezometers in a Cladium mariscus L. (Pohl) and Phragmites australis Cav. (Streud.) root mat in a UK fen. Tests were initiated by both slug insertion and slug withdrawal. Repeat tests were conducted on some piezometers to check for test consistency. Rapid recoveries after both slug insertion and withdrawal were found, with 90% recovery reached for all tests within 1500 s and for many within 300 s. We found significant and highly reproducible differences between recovery after insertion and recovery after withdrawal, with the latter being more rapid than the former. We invoke a reversible pore blocking mechanism to explain this behaviour. Many of the piezometers showed recoveries after withdrawal that were broadly consistent with the assumption of a rigid porous medium in which Darcy's law holds. Tests on four further piezometers were used to examine the impact of piezometer 'development', different slug sizes and the use of 'clean' water on test behaviour. The results from these test piezometers were difficult to interpret. Nevertheless, it appears that replacing 'dirty' water in the piezometer standpipe with clean water leads to more rapid recoveries and reduces the difference between recovery after insertion and recovery after withdrawal. The K of the root mat, as estimated from withdrawal tests on 14 piezometers and standardized to 20°C, ranged between 0Ð00144 and 0Ð03022 cm s1 . This appears to be at the very top end of K values reported for fen peats and suggests that water can flow readily through this medium given sufficiently large hydraulic gradients.