Influence of regional geology and hydrogeology on river habitat quality: examples from Mill Brook and Elderkin Brook, Kings County, Nova Scotia

Authors

  • Ian S. Spooner Department of Geology and Environmental Science Program, Acadia University, Wolfville, Nova Scotia BOP IPO, Canada
  • Heather Fenton Department of Geology and Geophysics, University of Calgary, Calgary, Alberta T2N 1N4, Canada
  • Melody Myers Geological Survey of Canada, Terrain Sciences Division, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada

DOI:

https://doi.org/10.4138/2049

Abstract

Elderkin Brook and Mill Brook are tributaries of the Cornwallis River and were investigated with the intent of understanding the geological conditions that could influence both habitat quality and river restoration efforts. The Cornwallis River and its tributaries have been the focus of restoration efforts in an attempt to re-establish brook trout (Sahelinus fontinalis) and Atlantic salmon (Salmo salar) populations. Both tributaries are relatively short, high-gradient headwater streams that are ungraded along much of their length. Data from Elderkin Brook indicate that pyrite-rich slate of the Kentville and Halifax formations that dominate the watershed geology do not govern the pH of the river discharge. The carbonaceous New Canaan Formation buffers regional groundwater and has resulted in elevated pH levels (7.5-8.0). Springs in the ungraded portion of Elderkin Brook introduce slightly acidic iron-rich groundwater into the system and, upon contact with the alkaline discharge, have produced sporadic masses of flocculated ferric hydroxide (Fe(OH)5). Along the upper reaches of Mill Brook, iron-rich acidic groundwater (pH 5.O-5.5) originating from the Kentville Formation influences the chemistry of the river discharge during low-flow conditions. However, groundwater input from the porous, calcareous-cemented Wolfville Formation that underlies the lower portion of Mill Brook has resulted in locally elevated pH levels (6.0-6.5) and the precipitation of extensive Fe(OH)5 deposits. In both Elderkin Brook and Mill Brook, the precipitation, deposition and preservation of ferric hydroxide is controlled by regional and local, geological and hydrogeological conditions. During the winter and spring, increased discharge and dilution of the groundwater chemistry by precipitation keep iron in either solution or suspension. During low-flow periods (primarily in the fall) flocculated ferric hydroxide accumulations develop coincident with the spawning of both fish species. These conditions result in both temporally and spatially constrained habitat degradation that may be difficult to recognise using the habitat evaluation techniques that are presently being employed by river management groups. RÉSUMÉ Le ruisseau Elderkin et le ruisseau Mill sont des affluents de la rivière Cornwallis; on les étudies dans le but de comprendre les conditions géologiques qui pourraient influer tant sur la qualité de l'habitat que sur les efforts de remise en état de la rivière. La rivière Cornwallis et ses affluents ont fait l'objet de travaux de remise en état visant à rétablir les populations d'ombles de fontaine (Salvelinus fontinalis) et de saumons atlantiques (Salmo salar). Les deux affluents sont des cours d'eau d'amont relativement peu étendus a forte déclivité et au lit accidenté sur une bonne partie de leur longueur. Les données provenant du ruisseau Elderkin révèlent que l'ardoise riche en pyrite des formations de Kentville et d'Halifax qui prédomine dans la structure géologique du bassin versant ne regit pas le pH du débit fluviatile. La Formation carbonée de New Canaan tamponne l'eau souterraine de la région et elle a entrainé des pH eleves (7,5-8,0). Les sources qui coulent dans la partie accidentée du ruisseau Elderkin introduisent de l'eau souterraine riche en fer légèrement acide dans le réscau et elles ont, au contact avec l'écoulement alcalin, produit des masses sporadiques d'hydroxy de ferrique [Fe(OH)5] floculé. Le long des sections supérieures du ruisseau Mill, l'eau souterraine acide riche en fer (pH de 5,0-5,5) en provenance de la Formation de Kentville influence la composition chimique du débit fluviatile à l'étiage. L'apport d'eau souterraine de la Formation a ciment calcaire poreux de Wolfville sous-jacente à la partie inférieure du ruisseau Mill a entrainé des pH localement élevés (6,0-6,5) et la precipitation de vastes dépôts de Fe(OH)5 Dans les ruisseaux Elderkin et Mill, la precipitation, la sedimentation et la conservation de l'hydroxyde ferrique sont fonction des conditions géologiques et hydrogeologiques régionales et locales. En hiver et au printemps, l'écoulement accru d'eau souterraine et la dilution de sa composition chimique due à la précipitation maintient du fer en place en solution ou en suspension. Pendant les périodes d'étiage (surtout l'automne), l'hydroxyde ferrique floculé s'accumule au moment de la periode de frayage des deux especés de poissons. Ces conditions entrainent une degradation de l'habitat qui est soumis à des contraintes temporelles et spatiales qu'il pourrait etre difficile de caractériser au moyen des techniques devaluation de l'habitat présentement employées par les groupes de gestion des rivières. Traduit par la rédaction

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Published

1998-10-01

How to Cite

Spooner, I. S., Fenton, H., & Myers, M. (1998). Influence of regional geology and hydrogeology on river habitat quality: examples from Mill Brook and Elderkin Brook, Kings County, Nova Scotia. Atlantic Geoscience, 34(3). https://doi.org/10.4138/2049

Issue

Vol. 34 No. 3 (1998)

Section

Articles

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