Temporal and spatial patterns in stream physicochemistry and insect assemblages in tropical lowland streams

A Ramirez, C PRINGLE, Michael Douglas

    Research output: Contribution to journalArticleResearchpeer-review

    Abstract

    Stream physicochemistry and insect assemblages were studied in lowland tropical streams in Costa Rica to determine physicochemical variables explaining temporal and spatial variations in insect density and biomass. Streams drained a tropical wet forest landscape and had similar geomorphology, but differed in their water chemistry because of differential inputs of solute-rich (i.e., P, Cl-, and Mg) geothermally modified groundwater. We hypothesized that, within a stream, physical factors, such as discharge, would result in temporal variation in insect assemblages, whereas interstream differences in solute composition would result in differences in insect assemblages among streams. Insect density, biomass, richness, and stream physicochemistry were measured monthly for 1 y in 6 streams. Insect samples were collected with a core sampler in runs where leaf litter overlying fine sediments was the main substrate. Streams with high inputs of geothermally modified groundwater had high conductivity and high concentrations of soluble reactive P (SRP). Annual temporal patterns in stream physicochemistry were related either to rainfall, with subsequent changes in discharge, or to the % geothermally modified groundwater entering streams. Streamwater pH decreased throughout the year, and unbuffered, nongeothermally modified streams changed from near neutral (pH >6) to near acidic (pH <4.5). In all streams, insect density and biomass were highest during the dry season and lowest during the wet season. Insect density and biomass were related positively to pH and to the number of days since the last storm. Insect taxonomic composition was similar among streams. Moreover, interstream variation in insect assemblages was small, and insect density and biomass were not related to any of the measured physicochemical variables, including SRP, which ranged from <5 to 267 ?g/L. Overall, the physicochemical characteristics of the study streams were related mainly to geothermally modified groundwater inputs and seasonal patterns in rainfall. Streams with geothermally modified groundwater inputs were better buffered against pH changes than the other streams. Insect assemblages reflected fluctuations in stream physicochemistry during the year and were associated with 2 main factors: floods and pH. Physicochemical characteristics were very different among streams, but insect assemblages were not related to them. We hypothesize that the heterogeneous nature of benthic substrata in the streams resulted in high variation in density and biomass of insects, potentially obscuring differences in insect assemblages among streams. � 2006 by The North American Benthological Society.
    Original languageEnglish
    Pages (from-to)108-125
    Number of pages18
    JournalJournal of the North American Benthological Society
    Volume25
    Issue number1
    Publication statusPublished - 2006

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    lowlands
    insect
    insects
    groundwater
    biomass
    solutes
    temporal variation
    solute
    core samplers
    rain
    streamwater
    rainfall
    geomorphology
    hydrochemistry
    leaf litter
    wet season
    plant litter
    water chemistry
    Costa Rica
    sampler

    Cite this

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    title = "Temporal and spatial patterns in stream physicochemistry and insect assemblages in tropical lowland streams",
    abstract = "Stream physicochemistry and insect assemblages were studied in lowland tropical streams in Costa Rica to determine physicochemical variables explaining temporal and spatial variations in insect density and biomass. Streams drained a tropical wet forest landscape and had similar geomorphology, but differed in their water chemistry because of differential inputs of solute-rich (i.e., P, Cl-, and Mg) geothermally modified groundwater. We hypothesized that, within a stream, physical factors, such as discharge, would result in temporal variation in insect assemblages, whereas interstream differences in solute composition would result in differences in insect assemblages among streams. Insect density, biomass, richness, and stream physicochemistry were measured monthly for 1 y in 6 streams. Insect samples were collected with a core sampler in runs where leaf litter overlying fine sediments was the main substrate. Streams with high inputs of geothermally modified groundwater had high conductivity and high concentrations of soluble reactive P (SRP). Annual temporal patterns in stream physicochemistry were related either to rainfall, with subsequent changes in discharge, or to the {\%} geothermally modified groundwater entering streams. Streamwater pH decreased throughout the year, and unbuffered, nongeothermally modified streams changed from near neutral (pH >6) to near acidic (pH <4.5). In all streams, insect density and biomass were highest during the dry season and lowest during the wet season. Insect density and biomass were related positively to pH and to the number of days since the last storm. Insect taxonomic composition was similar among streams. Moreover, interstream variation in insect assemblages was small, and insect density and biomass were not related to any of the measured physicochemical variables, including SRP, which ranged from <5 to 267 ?g/L. Overall, the physicochemical characteristics of the study streams were related mainly to geothermally modified groundwater inputs and seasonal patterns in rainfall. Streams with geothermally modified groundwater inputs were better buffered against pH changes than the other streams. Insect assemblages reflected fluctuations in stream physicochemistry during the year and were associated with 2 main factors: floods and pH. Physicochemical characteristics were very different among streams, but insect assemblages were not related to them. We hypothesize that the heterogeneous nature of benthic substrata in the streams resulted in high variation in density and biomass of insects, potentially obscuring differences in insect assemblages among streams. � 2006 by The North American Benthological Society.",
    keywords = "benthos, biomass, forest, groundwater, insect, stream, tropical region, Central America, Costa Rica, Hexapoda, Insecta, Invertebrata",
    author = "A Ramirez and C PRINGLE and Michael Douglas",
    year = "2006",
    language = "English",
    volume = "25",
    pages = "108--125",
    journal = "Journal of the North American Benthological Society",
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    Temporal and spatial patterns in stream physicochemistry and insect assemblages in tropical lowland streams. / Ramirez, A; PRINGLE, C; Douglas, Michael.

    In: Journal of the North American Benthological Society, Vol. 25, No. 1, 2006, p. 108-125.

    Research output: Contribution to journalArticleResearchpeer-review

    TY - JOUR

    T1 - Temporal and spatial patterns in stream physicochemistry and insect assemblages in tropical lowland streams

    AU - Ramirez, A

    AU - PRINGLE, C

    AU - Douglas, Michael

    PY - 2006

    Y1 - 2006

    N2 - Stream physicochemistry and insect assemblages were studied in lowland tropical streams in Costa Rica to determine physicochemical variables explaining temporal and spatial variations in insect density and biomass. Streams drained a tropical wet forest landscape and had similar geomorphology, but differed in their water chemistry because of differential inputs of solute-rich (i.e., P, Cl-, and Mg) geothermally modified groundwater. We hypothesized that, within a stream, physical factors, such as discharge, would result in temporal variation in insect assemblages, whereas interstream differences in solute composition would result in differences in insect assemblages among streams. Insect density, biomass, richness, and stream physicochemistry were measured monthly for 1 y in 6 streams. Insect samples were collected with a core sampler in runs where leaf litter overlying fine sediments was the main substrate. Streams with high inputs of geothermally modified groundwater had high conductivity and high concentrations of soluble reactive P (SRP). Annual temporal patterns in stream physicochemistry were related either to rainfall, with subsequent changes in discharge, or to the % geothermally modified groundwater entering streams. Streamwater pH decreased throughout the year, and unbuffered, nongeothermally modified streams changed from near neutral (pH >6) to near acidic (pH <4.5). In all streams, insect density and biomass were highest during the dry season and lowest during the wet season. Insect density and biomass were related positively to pH and to the number of days since the last storm. Insect taxonomic composition was similar among streams. Moreover, interstream variation in insect assemblages was small, and insect density and biomass were not related to any of the measured physicochemical variables, including SRP, which ranged from <5 to 267 ?g/L. Overall, the physicochemical characteristics of the study streams were related mainly to geothermally modified groundwater inputs and seasonal patterns in rainfall. Streams with geothermally modified groundwater inputs were better buffered against pH changes than the other streams. Insect assemblages reflected fluctuations in stream physicochemistry during the year and were associated with 2 main factors: floods and pH. Physicochemical characteristics were very different among streams, but insect assemblages were not related to them. We hypothesize that the heterogeneous nature of benthic substrata in the streams resulted in high variation in density and biomass of insects, potentially obscuring differences in insect assemblages among streams. � 2006 by The North American Benthological Society.

    AB - Stream physicochemistry and insect assemblages were studied in lowland tropical streams in Costa Rica to determine physicochemical variables explaining temporal and spatial variations in insect density and biomass. Streams drained a tropical wet forest landscape and had similar geomorphology, but differed in their water chemistry because of differential inputs of solute-rich (i.e., P, Cl-, and Mg) geothermally modified groundwater. We hypothesized that, within a stream, physical factors, such as discharge, would result in temporal variation in insect assemblages, whereas interstream differences in solute composition would result in differences in insect assemblages among streams. Insect density, biomass, richness, and stream physicochemistry were measured monthly for 1 y in 6 streams. Insect samples were collected with a core sampler in runs where leaf litter overlying fine sediments was the main substrate. Streams with high inputs of geothermally modified groundwater had high conductivity and high concentrations of soluble reactive P (SRP). Annual temporal patterns in stream physicochemistry were related either to rainfall, with subsequent changes in discharge, or to the % geothermally modified groundwater entering streams. Streamwater pH decreased throughout the year, and unbuffered, nongeothermally modified streams changed from near neutral (pH >6) to near acidic (pH <4.5). In all streams, insect density and biomass were highest during the dry season and lowest during the wet season. Insect density and biomass were related positively to pH and to the number of days since the last storm. Insect taxonomic composition was similar among streams. Moreover, interstream variation in insect assemblages was small, and insect density and biomass were not related to any of the measured physicochemical variables, including SRP, which ranged from <5 to 267 ?g/L. Overall, the physicochemical characteristics of the study streams were related mainly to geothermally modified groundwater inputs and seasonal patterns in rainfall. Streams with geothermally modified groundwater inputs were better buffered against pH changes than the other streams. Insect assemblages reflected fluctuations in stream physicochemistry during the year and were associated with 2 main factors: floods and pH. Physicochemical characteristics were very different among streams, but insect assemblages were not related to them. We hypothesize that the heterogeneous nature of benthic substrata in the streams resulted in high variation in density and biomass of insects, potentially obscuring differences in insect assemblages among streams. � 2006 by The North American Benthological Society.

    KW - benthos

    KW - biomass

    KW - forest

    KW - groundwater

    KW - insect

    KW - stream

    KW - tropical region

    KW - Central America

    KW - Costa Rica

    KW - Hexapoda

    KW - Insecta

    KW - Invertebrata

    M3 - Article

    VL - 25

    SP - 108

    EP - 125

    JO - Journal of the North American Benthological Society

    JF - Journal of the North American Benthological Society

    SN - 0887-3593

    IS - 1

    ER -