Serial discontinuity in naturally alternating forest and floodplain habitats of a Michigan (USA) stream based on physicochemistry, benthic metabolism, and organismal assemblages

Abstract

We tested the response of several different water quality metrics at 6 sites along a 4-km alternating forest (canopied) and floodplain (non-canopied) reach of the East Branch of the Black River, an undisturbed northern Lower Michigan trout stream, during summer 2015. Physicochemical parameters were unchanged between sites and reflected an undisturbed continuum. In-stream woody debris was higher at the forest sites, whereas relative canopy cover and sunlight intensity were higher at the floodplain sites. Both benthic macroinvertebrates and adult caddisflies exhibited greater species richness and a higher abundance of shredders at the forest sites, and a higher abundance of scrapers at the floodplain sites. Fish specimen abundance, species richness, and percentage of trout were not different between sites, and instead all increased throughout the summer. Community respiration was unchanged between the single tested floodplain site and the forest sites upstream and downstream of it. Gross primary production and net daily metabolism were higher at the floodplain site, leading to stream autotrophy. This result was also obtained when tested in summer 2017. Our results support the idea that terrestrial habitat changes can singularly affect the fundamental ecological functioning of an undisturbed stream, primarily due to deviations in sunlight penetration and allochthonous input. Moreover, the short distances between sites with alternating results indicate the dynamic and serially discontinuous state of natural rivers.

Comparison of caddisfly (Insecta, Trichoptera) assemblages from lake and river habitats of the Huron Mountains of Michigan (USA)

“…Specific conductance is a general indicator of nutrient, sediment, and organic matter concentrations ( Allan 2004 ). The values of HMC rivers were ~ 1/6 that of Michigan agricultural rivers ( Castillo et al 2000 ; Bernot et al 2006 ; Arango et al 2007 ; Houghton et al 2011 ) and ~1/3 that of other undisturbed Michigan rivers ( Houghton et al 2018 ), suggesting very low anthropogenic seston enrichment. Yanoviak and McCafferty (1996) found similar low specific conductance values when they sampled the Pine River, Mountain Stream, and the Salmon Trout River ~ 27 years ago.…”

“…The high relative biomass of shredders (~ 50%) relative to scrapers (< 10%) in lakes of the Huron Mountains demonstrated the importance of coarse allochthonous input to lake food webs. While only caddisflies were sampled in this study, several other studies have demonstrated that trends in caddisfly FFG ecology usually reflect those of the overall insect assemblage ( Mackay and Wiggins 1979 ; Dohet 2002 ; Houghton et al 2011 ; Houghton et al 2018 ; Morse et al 2019a ; Houghton 2021).…”

“…The known species richness of the Huron Mountains habitats represents > 50% of all 305 species found in Michigan ( Houghton et al 2018 ; Houghton 2020 ) and > 30% of all ~ 550 species found in the Upper Midwest region of the United States (Rasmussen and Morse 2018; Houghton et al 2022 ). The Huron Mountains habitats contained ~ 1.5 × as many caddisfly species (114) as the Black River Ranch of northern Lower Michigan, ~ 2.5 × that of Indiana Dunes National Lakeshore (64), and ~ 3.5 × that of Isle Royale National Park (46), other fairly undisturbed areas of Michigan and northern Indiana sampled with a rigorous effort ( DeWalt and South 2015 ; DeWalt et al 2016 ; Houghton 2016).…”

“…The caddisflies ( Trichoptera ) constitute a particularly important group of organisms for biological monitoring due to their high species richness, ecological diversity, and differing sensitivities to various anthropogenic disturbance ( Barbour et al 1999 ; Dohet 2002 ; Houghton 2008 ; Houghton et al 2011 ; Morse et al 2019a ). Although the caddisflies of Michigan are generally well known ( Houghton et al 2018 ), new species and state records continue to be found in under-collected regions ( Houghton 2020 ). Moreover, nearly all collections of the taxonomically important adult caddisflies in Michigan have consisted of a single sample from a collection site, usually an ultraviolet light trap deployed for a single evening.…”

Ash-free dry mass values for northcentral USA caddisflies (Insecta, Trichoptera)

“…Some challenges to using the immature stage, such as the difficulty of sampling all aquatic microhabitats representatively and identifying specimens to the species level, can be alleviated by using the winged adult stage, particularly that of taxonomically and ecologically diverse groups such as the caddisflies ( Trichoptera ) ( Gerth and Herily 2006 ; Chessman et al 2007 ; Cao and Hawkins 2011 ; Houghton et al 2011 ). Assemblages of caddisfly adults, particularly the relative abundance of specimens within different FFGs , have been shown in several studies to be indicative of stream conditions ( Dohet 2002 ; Houghton 2007 ; Blinn and Ruiter 2013 ; Houghton et al 2018 ). Such studies, however, treated all specimens equally and did not reflect the differences in biomass between different species.…”