[1] Raman spectra distributed temperature sensing (DTS) by fiber-optic cables has recently shown considerable promise for the measuring and monitoring of surface and near-surface hydrologic processes such as groundwater-surface water interaction, borehole circulation, snow hydrology, soil moisture studies, and land surface energy exchanges. DTS systems uniquely provide the opportunity to monitor water, air, and media temperatures in a variety of systems at much higher spatial and temporal frequencies than any previous measurement method. As these instruments were originally designed for fire and pipeline monitoring, their extension to the typical conditions encountered by hydrologists requires a working knowledge of the theory of operation, limitations, and system accuracies, as well as the practical aspects of designing either short-or long-term experiments in remote or challenging terrain. This work focuses on providing the hydrologic user with sufficient knowledge and specifications to allow sound decisions on the application and deployment of DTS systems.

We assembled data from a global network of automated lake observatories to test hypotheses regarding the drivers of ecosystem metabolism. We estimated daily rates of respiration and gross primary production (GPP) for up to a full year in each lake, via maximum likelihood fits of a free-water metabolism model to continuous highfrequency measurements of dissolved oxygen concentrations. Uncertainties were determined by a bootstrap analysis, allowing lake-days with poorly constrained rate estimates to be down-weighted in subsequent analyses. GPP and respiration varied considerably among lakes and at seasonal and daily timescales. Mean annual GPP and respiration ranged from 0.1 to 5.0 mg O 2 L 21 d 21 and were positively related to total phosphorus but not dissolved organic carbon concentration. Within lakes, significant day-to-day differences in respiration were common despite large uncertainties in estimated rates on some lake-days. Daily variation in GPP explained 5% to 85% of the daily variation in respiration after temperature correction. Respiration was tightly coupled to GPP at a daily scale in oligotrophic and dystrophic lakes, and more weakly coupled in mesotrophic and eutrophic lakes. Background respiration ranged from 0.017 to 2.1 mg O 2 L 21 d 21 and was positively related to indicators of recalcitrant allochthonous and autochthonous organic matter loads, but was not clearly related to an indicator of the quality of allochthonous organic matter inputs.Gross primary production (GPP) and respiration are perhaps the two most fundamental processes in ecosystems. At the cellular or organismal level, they describe biochemical pathways that make organic carbon molecules and energy available to cells. When these cellular processes are integrated across an entire ecosystem, the result-ecosystemlevel GPP, ecosystem respiration, or collectively ecosystem metabolism-describes biogeochemical and trophic processes occurring at the system level.There is substantial interest in understanding the controls on ecosystem metabolism in aquatic (Mulholland et al.

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A semantic model for overall welfare assessment of Atlantic salmon reared in sea cages is presented. The model, called SWIM 1.0, is designed to enable fish farmers to make a formal and standardized assessment of fish welfare using a set of selected welfare indicators. In order to cover all welfare relevant aspects from the animals’ point of view and to create a science‐based tool we first identified the known welfare needs of Atlantic salmon in sea cages and searched the literature for feasible welfare indicators. The framework of semantic modelling was used to perform a structured literature review and an evaluation of each indicator. The selected indicators were water temperature, salinity, oxygen saturation, water current, stocking density, lighting, disturbance, daily mortality rate, appetite, sea lice infestation ratio, condition factor, emaciation state, vertebral deformation, maturation stage, smoltification state, fin condition and skin condition. Selection criteria for the indicators were that they should be practical and measureable on the farm, that each indicator could be divided into levels from good to poor welfare backed up by relevant scientific literature. To estimate each indicator’s relative impact on welfare, all the indicators were weighted based on their respective literature reviews and according to weighting factors defined as part of the semantic modelling framework. This was ultimately amalgamated into an overall model that calculates welfare indexes for salmon in sea cages. More importantly, the model identifies how each indicator contributes (negatively and positively) to the overall index and hence which welfare needs are compromised or fulfilled.

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Chlorine 36 has many advantages as a dating tool for very old groundwater. These advantages include a suitable half-life (3.01 x l0 s years), simple geochemistry, conservative behavior in groundwater, and a general absence of subsurface sources at levels comparable to the atmospheric input. Recent advances in tandem accelerator mass spectrometry have permitted the analysis of 36C1 at the low abundance expected following residence in the subsurface for 106 years or more. In order to test the suitability of 36C1 for dating very old groundwater, the 36C1/C1 ratios of 26 groundwater samples from the Great Artesian Basin of Australia have been measured. Groundwater ages calculated from the 36C1 data compare favorably with ages computed independently from hydrodynamic simulations. INTRODUCTIONThe age of groundwater can be defined as the length of time the water has been isolated from the atmosphere. The concept of groundwater age is inherently somewhat ambiguous because, due to the effects of diffusion and hydrodynamic dispersion, no two water molecules in a given sample of water can be precisely the same age. Nevertheless, even though all samples are affected to some degree by mixing [Davis and Bentley, 1982], the concept of an "average" groundwater age is still a useful one. In this paper we compare two independent paethods of estimating this average groundwater age: (1) a new method of radiometric calculation dating, 36C1 tracing, and (2) the use of Darcy's law and the continuity equation.Up to the present time, the most successful radiometric method for the measurement of groundwater ages has been •4C dating. Carbon 14 dating of groundwater was first described by Munnich in 1957 and has since seen wide application. However, the inherent limitations of •'•C prevent its application in some circumstances where dating of groundwater is desired. One of these limitations is the age range over which dating is possible. With traditional direct-counting methods of measuring •4C, the maximum water age at which •4C can still be detected is less than 50,000 years. The advent of tandem accelerator mass spectrometry (TAMS) analysis and isotopic enrichment processes may advance this maximum age toward 80,000 years. Although this age limit is satisfactory for many shallow aquifers, deep regional flow systems commonly contain much older water. The need for a radio-nuclide with a longer half-life is particularly acute in hydrogeologic investigations of potential nuclear waste repositories in the deep subsurface. Such sites are intentionally located in low permeability formations containing very old water. Another disadvantage of •4C is the chemical reactivity of itsprincipal chemical form, the bicarbonate ion. The bicarbonate ion interacts with the aquifer matrix by precipitation or solution of carbonate minerals and exchange with carbonates, and is also produced biologically. These interactions complicate both determination of the initial •4C activity and the estimation of transport through the aquifer. A radioisotope with high sol...