Jeff Walker

Walker Environmental Research, LLC

With the rise of large-scale environmental models comes new challenges for how we best utilize this information in research, management and decision making. Interactive data visualizations can make large and complex datasets easier to access and explore, which can lead to knowledge discovery, hypothesis formation and improved understanding. Here, w...

Water level fluctuations (WLFs) affect phytoplankton dynamics, water quality, and fish populations in lakes and reservoirs around the world. However, such effects are system-specific and vary due to interactions with other external factors such as solar radiation, air temperature, wind, and external phosphorus loading. Utilizing data from a long-te...

As the number, size, and complexity of ecological data sets have increased, narrative and interactive raw data visualizations have emerged as important tools for exploring and understanding these large data sets. As a demonstration, we developed three visualizations to communicate and explore passive integrated transponder tag data from two long‐te...

Using nonparametric Mann-Kendall tests, we assessed long-term (1953-2012) trends in streamflow and precipitation in Northern California and Southern Oregon at 26 sites regulated by dams and 41 "unregulated" sites. Few (9%) sites had significant decreasing trends in annual precipitation, but September precipitation declined at 70% of sites. Site cha...

Recent developments in web technologies including evolution of web standards, improvements in browser performance, and the emergence of free and open-source software (FOSS) libraries are driving a general shift from server-side to client-side web applications where a greater share of the computational load is transferred to the browser. Modern clie...

We measured metabolism rates in a shallow, nitrogen-enriched coastal marine ecosystem on Cape Cod (MA, USA) during seven summers using an open-water diel oxygen method. We compared two basins, one directly receiving most of the nitrogen (N) load ("Snug Harbor") and another further removed from the N load and better flushed ("Outer Harbor"). Both di...

Water quality models of rivers often include three fundamental components: inflows and pollutant loads from point sources and watershed runoff, in-stream hydraulics, and in-stream water quality processes. In many cases, model development focuses mainly on the first and third components, while less attention is given to the in-stream hydraulics. An...

This study demonstrates how using different habitat models can influence the results of instream habitat assessment and conclusions for river management. We used three models for a portion of the Quinebaug River (Connecticut and Massachusetts, USA): a simplistic microhabitat model with univariate habitat-use criteria and substrate-based channel ind...

We used a simple laboratory experiment to investigate whether infiltration influences raindrop-impact induced soil erosion. There was substantially less erosion under infiltration conditions than with no infiltration. This was because a “shield” layer of deposited particles developed more rapidly under infiltration compared to “no-infiltration” con...

The recent rises in resident and tourist populations on St. John in the U.S. Virgin Islands have spurred the construction of new roads and housing developments throughout much of the island. As a result, a number of pollutants, including sediment and nitrogen, are being delivered to the coastal waters around the island at increasing rates and are b...

The rates of respiration, gross primary production, and net ecosystem production, referred to collectively as the whole ecosystem metabolism, were estimated for a shallow temperate estuary, West Falmouth Harbor on Cape Cod, MA, using the open-water diel oxygen method. We took continuous in situ measurements of dissolved oxygen levels at two sites w...

The rise in anthropogenic nutrient enrichment from coastal watersheds is causing degradation of estuaries worldwide through enhanced eutrophication. Understanding the response of the whole ecosystem metabolism to increased nutrient loading is critical for making informed management decisions regarding acceptable nutrient loading rates. We employed...