The Precipitationshed : Concepts, Methods, and Applications

Human societies are reliant on the functioning of the hydrologic cycle. The atmospheric branch of this cycle, often referred to as moisture recycling in the context of land-to-land exchange, refers to water evaporating, traveling through the atmosphere, and falling out as precipitation. Similar to the surface water cycle that uses the watershed as the unit of analysis, it is also possible to consider a ‘watershed of the sky’ for the atmospheric water cycle. Thus, I explore the precipitationshed - defined as the upwind surface of the Earth that provides evaporation that later falls as precipitation in a specific place. The primary contributions of this dissertation are to (a) introduce the precipitationshed concept, (b) provide a quantitative basis for the study of the precipitationshed, and (c) demonstrate its use in the fields of hydrometeorology, land-use change, social-ecological systems, ecosystem services, and environmental governance. In Paper I, the concept of the precipitationshed is introduced and explored for the first time. The quantification of precipitationshed variability is described in Paper II, and the key finding is that the precipitationsheds for multiple regions are persistent in time and space. Moisture recycling is further described as an ecosystem service in Paper III, to integrate the concept into the existing language of environmental sustainability and management. That is, I identify regions where vegetation more strongly regulates the provision of atmospheric water, as well as the regions that more strongly benefit from this regulation. In Paper IV, the precipitationshed is further explored through the lens of urban reliance on moisture recycling. Using a novel method, I quantify the vulnerability of urban areas to social-ecological changes within their precipitationsheds. In Paper V, I argue that successful moisture recycling governance will require flexible, transboundary institutions that are capable of operating within complex social-ecological systems. I conclude that, in the future, the precipitationshed can be a key tool in addressing the complexity of social-ecological systems. 

Dispersal in free-living, marine, benthic nematodes : passive or active processes?

Meiofauna, and especially marine nematodes are common in sediments around the world. Despite very wide ranging distributions in many nematode species, little is presently known about their dispersal mechanisms shaping these patterns. Rafting, and perhaps ballast water transport has been suggested as viable means for nematode long-range transport. On a much smaller scale other processes have been suggested for their dispersal. They generally include some form of passive suspension into the water column and later on a passive, haphazard settling back towards the bottom. Small-scale phenomena in nematode dispersal were studied by conducting a series of studies at Askö field station, Trosa Archipelago, Baltic proper. Studied aspects were one case of macrofaunal influence on nematode dispersal rate, using an amphipod, Monoporeia affinis as disturbing agent, and three different studies on mechanisms related to settling. The experiments were conducted both in laboratory and field settings. The amphipod Monoporeia affinis did not exert any influence on the dispersal rate in the nematodes. The nematode dispersal was only an effect of time, in the aspect that the more time that past, the more nematodes dispersed from their place of origin. The settling experiments revealed that nematodes do have an active component in their settling behaviour, as they were able to exert influence on the spot where they were to settle. They were able to choose settling spot in response to the food quality of the sediment. It also became evident that contrary to common belief, nematodes are able to extend their presence in the water column far beyond the times that would be predicted considering settling velocities and hydrodynamic conditions alone.