Altered Water and Nutrient Cycles:
LTER Network Research Initiative
Karen McGlathery, Jason Kaye
Overview: The theme of this workshop was refined to the following goal: Predict changes in the structure and function of the landscape as anthropogenic and natural disturbances to hydrological and biogeochemical cycles propagate across the earth.
This an integrative goal that easily lends itself to cross-site synthesis, has clear scientific and societal importance (ecological effects of changes in resource use, climate change), and can be addressed at multiple scales (within site, regional, national, international). Ultimately, all sites could be part of this synthesis, as all sites address some aspect of alterations of water and nutrient cycles. Several specific themes related to the larger goal emerged from the discussions: 1) multiple scales need to be addressed, including process-level studies, watershed approaches, models as linkages between sites and regions that have different drivers, and paleo/historical analyses; 2) predicting ecological responses to alterations of hydrological and biogeochemical cycles requires defining thresholds of critical ecological change; 3) links to socio-economic drivers are necessary, i.e., models/syntheses must incorporate humans into the landscape.
After a general discussion to define the workshop theme and approach, we broke out into small groups to discuss individual questions related to the overall theme. The charge for each group was to discuss: 1) how does the question relate to the overall theme?, 2) what relevant data exist?, 3) what relevant models exist?, 4) what experiments need to be done to address the question?, and 5) what linkages can be made to other proposed themes? What follows is a summary of the main ideas raised by each group.
How will future changes in land use/land cover affect water quality and quantity at large spatial/temporal scales, and how will this affect ecological and socioeconomic patterns and processes?
• Refining the question: Water “quality” is difficult to define; it is probably more appropriate to address the “delivery of water and matter.” Likewise, “land use/land cover” does not adequately reflect resource use, such as pumping of groundwater; instead address “land and resource use and cover.”
• Approach: The watershed approach, which is currently used at many LTER sites, is particularly appropriate for evaluating the delivery of water and matter over large spatial/temporal scales. Watershed scale (or other) analyses should be linked to 1) larger-scale drivers of land use change and 2) smaller-scale studies of internal processes (e.g., flow path analysis, hot spots and hot moments, in-stream processes). Integrative models that encompass mechanisms of land use change, watershed or landscape scale effects, and delivery to receiving waters will be important. Finally, paleo approaches may prove useful. It was suggested that we start with one or two questions that are focused and straightforward to address (achieve depth, then breadth), such as 1) how will residential land use change affect the ability of watersheds to retain atmospheric deposition?, and 2) what are the controls on denitrification across the landscapes in the LTER network?
• Inventory of available data and models: An important part of the planning grant would be to inventory what land use/land cover change work is currently being done in the network. Some examples are 1) sites that are studying land use/land cover change (e.g., BES, DAP, PIE, VCR, Harvard Forest), 2) sites that are evaluating indirect effects of regional land use change on atmospheric deposition (e.g., NWT, HBR), and 3) sites that are evaluating land use change in areas adjacent to their site (e.g., CWT, NTL, FCE). Experiments/manipulations: Everyone agreed that it would be essential to have some type of multi-site experiment and/or suite of measurements and/or analyses (e.g., stable isotopes), but because of the limited time, this question did not get addressed fully.
What are the ecological responses to increases in vigor of the hydrological cycle (e..g, more rainfall, more cloudiness, suppressed temperature extremes)?
• Refining the question: “Vigor” of the hydrological cycle was not considered to be the appropriate term; instead it was suggested that we focus on ecological responses to “alterations” of the hydrological cycle.
• Approach: More emphasis should be given to human-modified changes in the hydrological cycle (e.g., channelization), as this is easier to follow than climatic changes. Scaling is an important issue; most LTERs are too small to answer this question adequately, so regionalization is needed. We should interface with the USGS work on monitoring hydrological cycles, where we make the link to ecological patterns and processes. Finally, it is important to study governance and what determines land use pattern.
• Synthetic questions: What are the ecological responses to changes in the hydrological regime? What are the interactions between humans and hydrology?
Experiments/manipulations: Again, cross-site experiments were considered essential, but the group ran out of time before these ideas could be developed.
How has human
alteration of biogeochemical cycles changed ecosystem pattern and process? This group also discussed What is the role of climate variability on the
biogeochemistry of forested catchments?
• Approach: The goal is to define the patterns, gradients and thresholds in water quality/quantity and the rates/pathways of biogeochemical cycles. A cross-site comparison of carbon cycling impacts could serve as a synthesis of results as inputs to models.
• Themes: Accelerations of cycles of resources: N, P, H, S and water.
• Ideas for future workshop: Meta analysis needed of responses to altered hydrological/biogeochemical cycles (e.g., DOC leaching, trace gas emissions): 1) data gap analysis, 2) what experiments exist, what should be proposed, 3) what should the response variables be?, and 4) what is the relative importance of different drivers in different ecosystems?
Have changes in hydrological and biogeochemical cycles affected human use and perception of natural ecosystems?
• Approach:
The human response to changes in hydrological and biogeochemical cycles
is not preemptive; humans only react after a certain “catastrophic” threshold
has been reached in some response variable (e.g., water quality/quantity
parameter). It is therefore important to
predict these thresholds so that monitoring information can influence human use
and perception before catastrophic effects (thresholds) are reached. The question becomes how do we organize human
response and understand it across multiple scales from individuals to
communities to governments? From a human
use perspective, the response variables are similar to ecosystem services in a
landscape context: recreational suitability, aesthetics, habitat
quality for humans, food supply (agriculture and aquaculture), water supply,
flood control.
• Inventory of available data and models: A variety of data sets exist, including: 1)
state/national regulations (institutional decisions at the governmental level
about ecosystem management), 2) census data/demographics of human populations,
3) monitoring data from USDA, USGS, state geological surveys, agricultural
extension agencies, Division of Environmental Quality, 4) historical data
synthesizing human responses to water quality/quantity changes (e.g. start of
citizen action groups, regulations on line), and 5) monitoring data sets from
environmental groups (e.g., Parker River Clean Water group).
• Synthesis:
The goal of the synthesis work would be to develop empirical models to
predict thresholds for human response to alterations in hydrological and
biogeochemical cycles. We discussed a
case study approach addressing how land use changes have affected ecological
processes, comparing sites across the network.
Not every site would have to have the same land use issue in this
synthesis, as the questions in focus would be: Can threshold responses to
ecological change be quantified? Are
there ways to increase human awareness before (catastrophic) thresholds are
reached? Are there lag times before responses
occur to thresholds being reached? LTER
can do the following to address these questions: 1) surveys of people (defining
human response), 2) analyses of historical data (e.g., linkages of land use
change and water quality/quantity changes, model development), and 3)
education/awareness (e.g., SLTER). Examples where
historic data sets exist include studies on eutrophication,
acid rain, atmospheric nitrogen deposition, harmful algal blooms, and salt
water intrusion on groundwater quality.
Summary: We need
process-based predictive models to understand the ecological consequences of
human- and climate-driven alterations of hydrological and biogeochemical
cycles. We are currently “understanding
limited” not “data limited” in developing these models; we need synthetic,
multi-scale analyses to parameterize the models. Key questions are: What are the drivers of
change? What are the appropriate scales of study? What are the response
variables? What are the thresholds? How
do humans react to thresholds of ecological change?