DOI: 10.5061/dryad.sj3tx96fp
title: Agriculture land-use change seasonally rewires stream food webs: A case study from headwater streams in the Lake Erie watershed

description: Human impacts, like agricultural land-use change, alter natural patterns
 of resource availability and consumer response through space and time
 threatening the stability of ecosystems. In streams, removal of riparian
 zones and nutrient loading through agriculture may alter seasonal
 asynchronous resource fluxes and lead to food web rewiring and stability
 loss. Here, we seasonally sampled three streams across an agricultural
 gradient to determine how agricultural land-use change rewires seasonal
 stream food web structures. We show that agricultural land-use change
 seasonally rewired trophic interactions through reduced terrestrial energy
 use and trophic position. Additionally, agricultural land-use change drove
 steeper biomass size spectrum slopes and shifted fish communities to high
 abundances of small individuals. Collectively, our results suggest
 agricultural land-use change may be homogenizing stream food webs towards
 productive, single-energy channel dominated webs with faster turnover
 rates. Theory predicts such changes are indicative of instability,
 suggesting agriculture may be destabilizing stream food webs. Importantly,
 our results indicate agricultural land-use strategies that aim to retain
 riparian zones and reduce nutrient run-off may be important for reducing
 potential destabilizing effects. As agriculture is expected to increase to
 support growing human populations, elucidating strategies to maintain
 resilient stream food webs in agricultural landscapes is
 essential. 
description: # Agriculture land-use change seasonally rewires stream food webs: A case
 study from headwater streams in the Lake Erie watershed
 [https://doi.org/10.5061/dryad.sj3tx96fp](https://doi.org/10.5061/dryad.sj3tx96fp) ## Description of the data and file structure The study was conducted in three headwater streams (stream order = 3) along the north shore of Lake Erie, Ontario, a region with high cover of agricultural land. We collected seasonal stable isotope, stomach contents, fish community composition and supporting stream characteristic data from three streams spanning a gradient from low to high agricultural impact. For each stream, wetted width (cm), water depth (cm), and hydraulic head (estimate of relative flow velocity, cm) were measured twice a week from the beginning of May to the beginning of November 2018 (May 3, 2018 – November 5, 2018). Total nitrogen (N), total phosphorous (P) and % algal cover was measured at each of the streams monthly from June – August 2018.  Sampling of fish communities was conducted at each stream once in spring, summer, and fall 2018. Spring sampling was conducted May 28-30, summer sampling was conducted July 30-August 1, and fall sampling was conducted October 23-26. Fish were collected using a triple-pass electrofishing method based on the Ontario Stream Assessment Protocol Version 9.0. All fish caught were identified and weighed to examine fish community composition and biomass structure. From each stream, up to 20 creek chub were targeted and kept for analysis of stomach contents and stable isotopes. ### Files and variables #### File: fish\_baseline\_data.csv **Description:** all fish and baseline data (species, weights, stomach contents, raw stable isotope values). NA indicate information not available for given sample. ##### Variables * Season: season of sample collection (spring/summer/fall) * Date_yyyy_mm_dd: date of sample collection in format yyyy-mm-dd * SiteCode: unique site identifier (HC = low impact, EP4 = mid impact, AT = high impact) * Species_Code: unique species code * Common_Name: common name of fish species, baselines categorized into algae and detritus * Scientific_Name: scientific name of fish species, NA indicate no associated specific scientific name for algae/detritus * Number_of_Individuals: number of individuals in sample * Type: indicates whether measurement was done as part of individual or bulk sample. bulk samples have been separated so unique individual for each row. for bulk samples, individual weight determined as total weight of bulk sample/# of individuals in bulk sample. * Sample_ID: unique sample ID for individual samples, NA for bulk samples * Kept: indicates whether sample was kept or not (Y = yes, N = no). * SI_tissue_taken: indicates whether sample had SI tissue taken or not (Y = yes, N = no). * Weight_per_individual_g: weight if individual fish, in g. NA for baseline samples * Stomach_Contents: list of contents visually identified in stomach * Sampling_Type: indicates whether fish were collected via electrofishing, minnow trapping, or baselines for isotopes (algae and detritus) * d15N: raw d15N values * d2H: raw d2H values #### File: physical\_stream\_conditions.csv **Description:** wetted width, water depth and hydraulic head measurements from each stream ##### Variables * Date: date of stream measurement (dd/mm/yyyy) * Site_Code: unique site identifier (HC = low impact, EP4 = mid impact, AT = high impact) * Water_depth_cm: water depth measurement in cm * Hydraulic_head_cm: hydraulic head measurement in cm * Wetted_width_cm: wetted width measurement in cm #### File: summer\_algae\_cover.csv **Description:** summer % algal cover estimates ##### Variables * Site_Code: unique site identifier (HC = low impact, EP4 = mid impact, AT = high impact) * Month: month in 2018 that estimate was made * Algae_Coverage_percent: percent algal cover range category * Algae_Coverage_Category_Midpoint: midpoint in percent algal cover range category #### File: summer\_nutrient\_data.csv **Description:** summer nutrient concentrations of Nitrogen and Phosphorous ##### Variables * Site_Code: unique site identifier (HC = low impact, EP4 = mid impact, AT = high impact) * Sample_Date: date of water sample collection for nutrient analysis (dd-mm-yy) * TN_mg_per_L: total nitrogen (mg/L) * TP_mg_per_L: total phosphorous (mg/L) ## Code/software Code Files: seasonal_stream_morphology.R &lt;-- code to calculate seasonal mean and sd of water depth, wetted width and hydraulic head summer_nutrient_algae_mean.R &lt;-- code to calculate summer mean and sd of N, P and % algal cover trophic_group_proportions.R &lt;-- code to calculate proportion of trophic groups in streams based on visual stomach content identification baseline_outliers.R &lt;-- code to determine outliers in stable isotope baselines coupling_tp_analysis.R &lt;-- code to calculate seasonal % terrestrial energy use and trophic position of creek chub isotopic_niche_analysis.R &lt;-- code to calculate estiamtes of seasonal isotope niche space and overlap for creek chub figure_2 &lt;-- code to generate figure 2 (combine % terrestrial energy use, trophic position, and isotopic niche plots) fish_size_spectrum_MLE.R &lt;-- code to calculate size spectrum slopes using MLE methods adapted from Edwards et al., 2017, Methods in Ecology and Evolution, 8:1, 57-67 All code conducted in R v 4.4.2 ## Access information Other publicly accessible locations of the data: * [https://github.com/mariegutgesell/ag_seasonal_rewiring_MS](https://github.com/mariegutgesell/ag_seasonal_rewiring_MS) Data was derived from the following sources: * All data was collected as part of the study