nsink

Statement of need

The nsink package is an R implementation of the methods described in Kellogg et. al (2010). Previous implementation of this approach relied on a manual, vector based approach that was time consuming to prepare. This approach uses a hybrid raster-vector approach that takes relatively little time to set up for each new watershed and relies on readily available data. Total run times vary, but range from minutes up to 5 hours depending on options selected. Previous versions took weeks of manual data manipulation. Thus, nsink was developed to satisfy the need for quicker implementation of the NSink method as described in Kellogg et. al (2010).

nsink functionality

As of 2022-03-14 user functions for the nsink package are:

• nsink_get_huc_id(): A function for searching the name of a USGS Watershed Boundary Dataset Hydrologic Unit (https://www.usgs.gov/core-science-systems/ngp/national-hydrography/watershed-boundary-dataset) and retrieving its 12-digit Hydrologic Unit Code (HUC).
• nsink_get_data(): Using any acceptable HUC ID (e.g. 2-digit to 12-digit), this function downloads the NHDPlus, SSURGO, NLCD Land Cover, and the NLCD Impervious for that HUC.
• nsink_prep_data(): nsink needs data in a common coordinate reference system, from mutliple NHDPlus tables, and from different portions of SSURGO. This function completes these data preparation steps and outputs all data, clipped to the HUC boundary.
• nsink_calc_removal(): Quantifying relative N removal across a landscape is a key aspects of an nsink analysis. The nsink_calc_removal() function takes the object returned from nsink_prep_data() and calculates relative N removal for each landscape sink. See Kellogg et al [-@kellogg2010geospatial] for details on relative N removal estimation for each sink.
• nsink_generate_flowpath(): This function uses a combination of flow determined by topography, via a flow-direction raster, for the land-based portions of a flow path and of downstream flow along the NHDPlus stream network.
• nsink_summarize_flowpath(): Summarizing removal along a specified flow path requires relative N removal and a generated flow path. This function uses these and returns a summary of relative N removal along a flow path for each sink.
• nsink_generate_static_maps(): This function analyzes N removal at the watershed scale by summarizing the results of multiple flow paths. Four static maps are returned: 1)removal efficiency; 2)loading index; 3)transport index; 4)delivery index. Removal efficiency is a rasterized version of the nsink_calc_removal() output. Loading index is N sources based on NLCD categories. Transport index is a heat map with the cumulative relative N removal along flow paths originating from a grid of points, density set by the user, across a watershed, highlighting the gradient of downstream N retention. Delivery index is the result of multiplying the loading index and the transport index, and shows potential N delivery from different sources, taking into account the relative N removal as water moves downstream.
• nsink_plot(): A function that plots each raster in the list returned from nsink_generate_static_maps().
• nsink_build(): One of the drivers behind the development of the nsink package was to provide n-sink analysis output that could be used more broadly (e.g. within a GIS). The nsink_build() runs a complete nsink analysis and outputs R objects, shapefiles and/or TIFFs.
• nsink_load(): Essentially the inverse of the nsink_build() function, this function takes a folder of files, likely created by nsink_build(), and reads them into R.

Installation instructions

At this time we plan on maintaining the nsink package as a GitHub only package and thus it won’t be available directly from CRAN. You may use the install_github() function from the remotes package to install it. The code below will take care of installing remotes and installing nsink from the GitHub repository.

install.packages("remotes")
remotes::install_github("usepa/nsink", dependencies = TRUE, build_vignettes = TRUE)

And then to load up the package:

library(nsink)

Documentation and examples

All functions are documented, with examples, and that documentation may be accessed, in R, via the usual help functions. Additionally, an introduction to the nsink package with a more detailed workflow is documented in a vignette.

# Load up package
library(nsink)

# Access package level help
help(package = "nsink")

# Access the Introduction to nsink vignette
vignette("intro", package = "nsink")

Contributing

If you would like to contribute to the nsink package, please first read the CONTRIBUTING. In short, contributions are happily accepted either via suggestions in the Issues or via pull request.