The land-use legacy effect: Towards a mechanistic understanding of time-lagged water quality responses to land use/cover

Abstract

Numerous studies have linked land use/land cover (LULC) to aquatic ecosystem responses, however only a few have included the dynamics of changing LULC in their analysis. In this study, we explicitly recognize changing LULC by linking mechanistic groundwater flow and travel time models to a historical time series of LULC, creating a land-use legacy map. We then illustrate the utility of legacy maps to explore relationships between dynamic LULC and lake water chemistry. We tested two main concepts about mechanisms linking LULC and lake water chemistry: groundwater pathways are an important mechanism driving legacy effects; and, LULC over multiple spatial scales is more closely related to lake chemistry than LULC over a single spatial scale. We applied statistical models to twelve water chemistry variables, ranging from nutrients to relatively conservative ions, to better understand the roles of biogeochemical reactivity and solubility on connections between LULC and aquatic ecosystem response. Our study illustrates how different areas can have long groundwater pathways that represent different LULC than what can be seen on the landscape today. These groundwater pathways delay the arrival of nutrients and other water quality constituents, thus creating a legacy of historic land uses that eventually reaches surface water. We find that: 1) several water chemistry variables are best fit by legacy LULC while others have a stronger link to current LULC, and 2) single spatial scales of LULC analysis performed worse for most variables. Our novel combination of temporal and spatial scales was the best overall model fit for most variables, including SRP where this model explained 54% of the variation. We show that it is important to explicitly account for temporal and spatial context when linking LULC to ecosystem response.

Quantifying Landscape Nutrient Inputs With Spatially Explicit Nutrient Source Estimate Maps

“…In contrast to the success of reducing point sources, nonpoint source inputs remain high as they are not regulated in a similar manner. An additional concern with high input rates of nonpoint sources is the presence of land use legacies that can result in decades of delay before improvements to surface water concentrations are observed (Martin et al, , ; Meals et al, ; Ray et al, ; Van Meter & Basu, ; Verhougstraete et al, ).…”

“…result in decades of delay before improvements to surface water concentrations are observed (Martin et al, 2011(Martin et al, , 2017Meals et al, 2010;Ray et al, 2012;Van Meter & Basu, 2015;Verhougstraete et al, 2015).…”

Modeling how land use legacy affects the provision of ecosystem services in Mediterranean southern Spain

“…Martin et al [5] defined legacy effects as those effects from prior human disturbances that are still propagating through the ecosystem. In particular, historical human-induced land use changes may result in underpinning legacy processes that influence current ecosystem functioning and structure, biodiversity and ES.…”

“…While the ES bundles and scenarios approach has proven to be a powerful tool to enable better regional-scale land use decisions [4], so far, these approaches ignore the critical role that land use legacies play in understanding ES provision, i.e. effect from prior land use that are still propagating through the ecosystem [5].…”

“…For instance, Locatelli et al [12] reviewed existing literature and introduced the concept of land use trajectories as a mean of 'pathways of land change' that influence ES over time for mountain systems. Martin et al [5] developed a novel method to measure land use legacy for a single ES (i.e. water quality) in lake ecosystems.…”