Statistical Investigation of Climate Change Effects on the Utilization of the Sediment Heat Energy

Suvilahti, a suburb of the city of Vaasa in western Finland, was the first area to use seabed sediment heat as the main source of heating for a high number of houses. Moreover, in the same area, a unique land uplift effect is ongoing. The aim of this paper is to solve the challenges and find opportunities caused by global warming by utilizing seabed sediment energy as a renewable heat source. Measurement data of water and air temperature were analyzed, and correlations were established for the sediment temperature data using Statistical Analysis System (SAS) Enterprise Guide 7.1. software. The analysis and provisional forecast based on the autoregression integrated moving average (ARIMA) model revealed that air and water temperatures show incremental increases through time, and that sediment temperature has positive correlations with water temperature with a 2-month lag. Therefore, sediment heat energy is also expected to increase in the future. Factor analysis validations show that the data have a normal cluster and no particular outliers. This study concludes that sediment heat energy can be considered in prominent renewable production, transforming climate change into a useful solution, at least in summertime.

Warming of water temperature in spring and nutrient release from sediment in a shallow eutrophic lake

We investigated whether recent springtime water temperature increases in a shallow eutrophic lake affected bottom sediment temperature and fluxes of ammonia (NH4+) and phosphate (PO43−) from the sediment. We conducted a lake-wide survey of Lake Kasumigaura, Japan, and analyzed the relationship between water temperature increases in spring and NH4+ and PO43− release fluxes. We also developed a numerical model to analyze how water temperature increase affects sediment temperature. Water temperature in May increased during 2010–2019 at a rate of 1.8–3.2 °C decade−1. The numerical simulation results showed that the water temperature increase was accompanied by a sediment temperature increase from a minimum of 18.3 °C in 2011 to a maximum of 21.6 °C in 2015. Despite the substantial difference in the observed sediment temperature (2.9 °C), no significant differences in NH4+ and PO43− fluxes in May between 2013/2014 and 2015 were found. These results suggest that both water and sediment temperatures are increasing in Lake Kasumigaura in spring, but it is unclear whether this warming has affected NH4+ and PO43− releases from the sediment. However, because a nonlinear response to sediment temperature was observed, future springtime warming may accelerate NH4+ and PO43− releases.

Seasonal Variations in Bottom Water Temperatures and their Influence on Subaquatic Permafrost Thermal Regimes

<p>The thermal regime in sediment below the ocean or lakes is mostly governed by the sea or lake bed temperature and by the geothermal heat flow. This thermal regime will determine whether permafrost beneath water bodies is preserved or how rapidly it thaws. Thermal modelling uses mean annual bottom water temperatures to calculate permafrost presence or absence, while predictions of shallow sediment thermal regimes must be forced with time series of changing bottom water temperatures that also account for freezeback of the water column to the bottom, forming bottom-fast ice. However, continuous, annual measurements of bottom water temperatures in Arctic lakes and coastal marine settings are hard to obtain and therefore scarce. Waves and sea ice movement make deployment and recovery of instruments difficult.</p><p>We provide a parameterization of the bottom water temperature function that relies on easier to obtain variables, such as the mean, minimum and maximum air temperature and the water depth, by comparing measured and modelled shallow sediment thermal regimes from the Arctic. We use a parameterization based on a simple cosine for the water temperature with mean temperature, amplitude and time shift and add the minimum water temperature to obtain a 4 parameter function. For shallow regions with bottom-fast ice, additionally the duration of the ice-growth and -melting period as well as the minimum air temperature are needed.</p><p>We test our parameterizations with a globally unique data set of 4 years of ground temperature data collected from the seabed to a depth of 10 m from the near shore zone of the Mackenzie Delta. At the instrumented sites, permafrost is present beneath mostly freshwater bottom-fast and floating ice. Forward modeling of sediment temperatures is performed using the 1D heat transfer model CryoGrid with depth dependent thermal properties. We neglect advective processes and long-term temperature trends in the bottom water temperatures.</p><p> </p><p>Rough parameterization of the annual variation of water bottom temperatures reproduce measured water temperatures with a RMSE of 20-40 %. The resulting modeled sediment temperature field based on 10 years of repeated parameterized bottom water temperatures matches the modeled sediment temperature field based on measured water temperatures in terms of permafrost characteristics, including the depth of the active layer defined by the 0°C isotherm over the year. However, both modelled temperature fields yield significantly higher sediment temperatures than the measured sediment temperature field. This may be the result of choice of sediment thermal properties in the thermal model or shifts in the duration of bottom-fast ice contact or on-ice snow Since modelled temperature fields from both repeated measured and parameterized bottom water temperatures show the same deviation, it suggests that the bottom water temperatures were warmer during the measurement period than the average over the previous 10 years.</p>

The effect of sediment thermal conductivity on vertical groundwater flux estimates

Vertical sediment temperature profiles are frequently used to estimate vertical fluid fluxes. In these applications using heat as a tracer of groundwater flow, the thermal conductivity of saturated sediments (ke) is often given as a standard literature value and assumed to have a homogeneous distribution in the vertical space. In this study vertical sediment temperature profiles were collected in both a high-flux stream and a low-flux lagoon environment in sand- and peat-covered areas. ke was measured at the location of each temperature profile at several depths below the sediment–water interface up to 0.5 m with a measurement spacing of 0.1 m. In general ke values measured in this study ranged between 0.55 and 2.96 W m−1 ∘C−1 with an increase with depth from the sediment–water interface. The effect of using a vertically homogeneous or heterogeneous distribution of measured ke values on vertical flux estimates was studied with a steady-state HydroGeoSphere model. In the high-flux stream environment estimated fluxes varied between 0.03 and 0.71 m d−1 and in the low-flux lagoon between 0.02 and 0.23 m d−1. We found that using a vertically heterogeneous distribution of sediment thermal conductivity did not considerably change the fit between observed and simulated temperature data compared to a homogeneous distribution of ke. However, depending on the choice of sediment thermal conductivities, flux estimates decreased by up to 64 % or increased by up to 75 % compared to using a standard ke sediment thermal conductivity for sand, frequently assumed by previous local studies. Hence, our study emphasizes the importance of using spatially distributed thermal properties in heat flux applications in order to obtain more precise flux estimates.

The effect of sediment thermal conductivity on vertical groundwater flux estimates

Vertical sediment temperature profiles are frequently used to estimate vertical fluid fluxes. In these applications using heat as a tracer of groundwater flow, the thermal conductivity of saturated sediments (ke) is often given as a standard literature value and assumed to have a homogeneous distribution in the vertical space. In this study vertical sediment temperature profiles were collected both in a high-flux stream and a low-flux lagoon environment in a sand-, and peat-covered area. ke was measured at the location of each temperature profile at several depths below the sediment-water interface up to 0.5 m with a measurement spacing of 0.1 m. In general ke values measured in this study ranged between 0.55 and 2.96 W m−1 °C−1 with an increase with depth from the sediment-water interface. The effect of using a vertically homogeneous or heterogeneous distribution of measured ke values on vertical flux estimates was studied with a steady-state HydroGeoSphere model. In the high-flux stream environment estimated fluxes varied between 0.03 and 0.71 m d−1 and in the low-flux lagoon between 0.02 and 0.23 m d−1. It was found, that using a vertically heterogeneous distribution of sediment thermal conductivity did not considerably change the fit between observed and simulated temperature data compared to a homogeneous distribution of ke. However, depending on the choice of sediment thermal conductivities, flux estimates decreased by up to 64 % or increased by up to 75 % compared to using a standard ke sediment thermal conductivity for sand, frequently assumed by previous local studies. Hence, our study emphasizes the importance of using spatially distributed thermal properties in heat flux applications in order to obtain more precise flux estimates.