The Eel River Critical Zone Observatory: exploring how the critical zone will mediate watershed currencies and ecosystem response in a changing environment

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The Eel River Critical Zone Observatory: exploring how the critical zone will mediate watershed currencies and ecosystem response in a changing environmentSurprisingly, we need to look inside hillslopes to understand variations in atmospheric moisture, the magnitude and chemistry of river flows, the dynamics of ecosystems, and, even coastal ocean productivity. These connections arise in a deep, unexplored landscape of weathered bedrock, populated by microbes, that lies beneath the hillslope surface and below the soil mantle and above a fresh bedrock boundary. Rain and snow melt can penetrate this weathered bedrock, be held as rock moisture and be exploited by trees, which return this moisture to the atmosphere through release (transpiration) from leaves. Bedrock properties influence how much moisture is available to plants, so in turn may determine which species can persist, especially in seasonally dry environments. The water released by trees influences air humidity and temperature, and the tree type affects how much solar energy is reflected or absorbed. Collectively these feedbacks influence atmospheric energy and circulation (and momentum). Rain and snow melt also penetrate to the underlying fresh bedrock boundary where water perches and flows as groundwater to streams through the weathered bedrock. This can control the timing, magnitude, and chemistry of runoff to rivers, especially during summer low flow periods. Hence, river ecosystems and the coastal oceans (where rivers discharge) are recipients of water and nutrients derived from deep inside hillslopes. The entire zone from vegetation canopy down through the soil and weathered bedrock to the start of fresh bedrock is referred to as the ?critical zone.? This zone mediates these ?watershed currencies?-- water, sediment, solutes (dissolved elements in water), gases, organisms, energy and momentum?that are exchanged and transformed in the course of biological and physical interactions across landscapes. PIs propose to establish the Eel River Critical Zone Observatory in Northern California for intensive field investigations of key mechanisms controlling these currencies and their consequences for water resources and ecosystem sustainability. Eel River CZO scientists will build models to explore how these currencies are exchanged among atmosphere, hillslopes, rivers and coastal oceans to investigate fundamental questions and to provide guidance for management issues. PIs identify four key frontier questions: 1) Do plants in seasonally dry environments rely on moisture from the weathered bedrock beneath the soil and if so how might bedrock properties then affect this availability and thus the resilience of vegetation to climate change? 2) As moisture conditions change, how do microbes in the critical zone influence the water chemistry and gasses discharged from hillslopes? 3) What controls the spatial extent of channels that remain wet (standing or flowing water) in the network of channels draining seasonally dry environments? and 4) Will changes in critical zone currencies, induced by climate or land use change, lead to sudden shifts in river and coastal ecosystems? Motivated by anticipated increase in climate extremes (especially extended drought) and accelerating societal demand for water, PIs focus on filling knowledge gaps that not only inhibit our ability to forecast the magnitude of future change of systems, but even the sign of that change. The Eel River CZO will be locally rooted in the Angelo Coast Range Reserve (in Northern California), but will extend to watershed and regional scales. It will be dedicated to detecting, explaining, and predicting driving mechanisms that connect watershed currencies to processes that operate in the critical zone. We will also develop a model which will provide local predictions over a regional scale that can be used to ask "what if" questions about possible future climate and landuse scenarios, and the consequences for runoff and ecosystem conditions.The Eel River CZO will produce a generation of students and postdocs who have worked together across the disciplines of climate science, hydrology, ecology, geobiology, geochemistry and geomorphology and who have made discoveries at the interface of these fields. There will be strong interactions with other CZOs. PIs will actively work with resource managers and watershed residents to share and generate knowledge and collaborate to build resource and ecosystem resilience, specifically in the Eel and Russian River coastal watersheds. They will focus on these watersheds, but anticipate our findings and modeling will then be expanded to a much broader region. Environmental change will come: the need for well-informed guidance and tools will accelerate. It is only through coupling mechanistic field studies and integrated modeling as proposed here that we can forecast and offer tools for decision makers to guide the future state of landscapes and their ecosystem functions and services