Freshwater Ecology Final Paper Comparing abundance and richness of BMIs to riffle and glide stream habitat types along the Tuolumne River Watershed.
Anthony Darretta AbstractThe distribution and diversity of aquatic insects were studied among four stream bed locations along the Tuolumne River in Waterford, CA. The Tuolumne River watershed is home to a variety of benthic macro invertebrates, many of which spend a majority of their lifecycles embedded within cobble beds and substratum. In this paper we can observe how riffle and glide stream types can influence how many types of aquatic insects will inhabit the sections, at what depths they may prefer to inhabit and whether or not cobble size and substratum influences these numbers. Observed patterns of abundance and richness show taxa and their relation to the stream sections they prefer to inhabit in this freshwater community. Introduction Along the stretches of the Tuolumne River through Waterford, CA there are large deposits of gravel bars which cause the stream to meander through and around them, resulting in section of riffle and glide flow habitats. Storage of fine sediment (particle sizes <2mm median diameter) within these gravel and cobble beds create optimal feeding and resting habitat for a variety of benthic macroinvertebrates (BMIs) who occupy specific niches within functional feeding groups (FFGs). FFGs are classifications that provide us with information on the balance of feeding relationships and strategies within and around the aquatic community including fish, insects and other invertebrates. Functional feeding groups include the filtering and gathering collectors (blackflies, caddisflies), shredders (scuds), scrapers (mayflies) and predators (dragonflies, damselflies).
The FFGs represent a simplified system model for more complex processes of trophic interactions for the production, consumption and decomposition of food resources. Any instabilities or trophic collapses that result in a stream ecosystem usually stem from an imbalance in these FFG relationships (Nakano 1999).Sediment retention around and underneath cobble and gravel rocks within riffles and glides provide these BMIs with adequate hiding spots from predation as well as a constant flow of nutrients being transported downstream. We took measurements from these two stream flow habitats and compared how different assemblages of BMIs correlated to them.The results of our observational study differentiate between the riffles and glides and what organisms preferred which habitat type, if any such lifestyle preference existed.
We extracted organisms from each habitat type and correlated them with water depth and cobble size.Methods and MaterialsField materials brought to the Tuolumne River Waterford site included 4 L plastic tubs, plastic vials containing 70% ethanol solution, meter sticks, D-frame collection nets, Write in the Rain notebooks and pencils, forceps and droppers.Stream macroinvertebrates were collected by disturbing the bottom sediment and cobble stones, either by hand picking stones and softly rubbing the material off the bottom and sides while holding it under the water level, or by agitating the sandy materials in the vacant locations with stone sizes less than 4cm in length. In both cases the stream flow brought the deposits into a D-frame net which was positioned directly downstream into the bed.
Substratum materials and benthic macroinvertebrates were then dislodged and taken into the net. More often than not, substratum material far outweighed the number of targeted organisms caught in the net and had to be manually separated.Inverting the net into a small plastic tub of water and gently washing out the material generally separated the sand particles and woody material from the organisms which aided in the insect collection. While the D ring net was held perpendicular to the flow it quickly became clogged against the inside net surface and resulted in backwash of the particle collection as the flow could not readily pass through netting; filtered materials were stirred out and resulted in loss, resulting in a source of error for average collection yield. Riffle and glide flow habitat types were denoted as separate collection sites and special care was taken to ensure collection methods did not differentiate between the two.
Glide habitats were deeper (stream beds usually ? 15 cm deep) and cobble stone handling as well as D-ring net placement was generally a two-person job, as the deeper water made it difficult to both handle the stones and keep the net in place. Riffle habitats were easier to collect at without assistance as stream depth was shallower (usually ? 10 cm deep) and flow rates were calmer. Visibility was reduced in comparison but by careful placement of the net downstream from the cobbles examined we were able to collect samples with ease.Once a sufficient amount was collected after extracting the D-ring net (net kept submerged between 15 – 20 seconds) organisms and substrate was washed into a small plastic tub.
Organisms were manually removed by hand (insects ? 1cm long) or by sucking out with a plastic dropper (insects < 1 cm long). Careful measures were taken as not to destroy the samples during this process. Samples removed from the wash tub were placed into plastic vials with 70% ethanol solution and allowed to remain in a cool environment as to remain undisturbed for later identification. In order to reduce inconsistencies between catch sites, five locations were taken into consideration with five cobble stones removed and rubbed clean, with the vacancies in the stream bed disturbed by hand. The integrity of nonrandom distributions in invertebrates was kept by making sure that large numbers of samples were collected in the net each time. Field sorting was loosely applied at this point in the collection process but was generally reserved for the lab.Sorting and identification of the insects usually took place in the lab room.
Further separation of mineral deposits, sandy/materials, leaves and woody particles from the target organisms required removing substrate in smaller batches from the plastic tubs and/or plastic vials and then by using needle nose tweezers to place into petri dishes. Microscopes were then used to further identify individual organisms and classify them based off physical attributes. Insects collected at the Tuolumne River Waterford site included larvae of caddisflies, stoneflies, damselflies, mayflies. Dichotomous keys were used in this identification process, especially for the organisms only visible through the microscope lens. Species diversity was documented with Excel sheets, as well as quantifying the selected taxa mean quantity, abundance of the sample site organisms overall as well as individual net captures for the selected cobble stones, and taxa richness.ResultsWhen comparing cobble size to BMI richness in glide flow habitats, we saw no clear correlation between the two measured parameters. Mean abundance did show that there was on average 14 BMIs on each cobble but the distribution of these did not relate to any specific cobble size.
(Table 1). When comparing cobble size to BMI richness in riffle flow habitats we saw a very clear relationship between the two (Table 2). A wide spread in distribution with smaller cobbles having a much less diverse array of BMIs and much larger cobbles having a wider array of BMIs and a greater richness therein. We expected there to be an increased richness and abundance together in these riffle cobble sections, but this trend towards greater richness may point to multiple FFGs benefitting from the riffles as opposed to a selective FFG being the sole inhabitant. When comparing water depth to BMI abundance in riffle flow habitats we saw that there was a stronger correlation between shallow stream sections (between 8cm – 16cm) having a higher abundance of BMIs than when compared with glides. Abundance in glides showed no indication that water depth played a role in affecting abundance.
In both cases, we compared these to cobble sizes in the stream type and there was a slight trend towards increased abundance with larger cobble When comparing water depth to BMI richness in riffle flow habitats we could see a trend towards cobbles having a greater richness in collected samples of BMIs at depths between 5 cm and 10 cm, with less richness > 10 cm depth. In comparison with BMI richness in the glide habitats, we saw a stronger correlation. In glide habitats, there was no statistical indication that water depth had any influence on richness. DiscussionCobble size did correlate to BMI richness in glide habitats as well as in riffles, with cobbles roughly 80 cm on average being home to 15 to 20 species of BMIs. We suspected that the cobbles with greater diameters would directly relate to a greater number of invertebrates attached to it, but this was not the case. The fact that cobble size in these riffle habitats related to richness of the samples collected was puzzling; we expected a uniform relationship between both abundance and richness. Richness measurements in this case reflect the diversity of species in aquatic assemblage living attached to the bottom of these cobbles and embedded in the sandy stream bed underneath. This increase in diversity pointed to a possible link between number of samples collected to the overall health of the niche space and food resources provided by the stream (Jones 2012).
The propagation of more species in both stream flow habitat types indicates that water depth played a less significant role than the sizes of the cobbles themselves, as mean temperatures between the two types had little to no variation indicating that the depth spread was not a determining factor in overall temperature variance. BMIs with different temperature tolerances did not reflect in any dataset here.We do see that the data representing the relationship between water depth and abundance showed a greater abundance of BMIs in riffle habitats than the glides. Water depth seemed to have played a significant role in determining how many insects we collected at the riffles, as greater depths (> 16 cm) yielded far fewer macroinvertebrates than the shallower locations whose abundances had a mean distribution of 26 specimens per cobble. However, richness would have served a stronger indicator that water depth (and temperature) provided a more stable niche for certain taxa. Abundance of specimens was not interpreted to be directly caused from depth but rather the size of the cobbles. Surface area directly affected the specimen count. Cobbles with B-axis length between 75mm and 100mm had roughly 45-55% greater richness than cobbles between 55mm and 70mm in riffle stream sections.
This could point to the same determining factor which corelates cobble size to species abundanceWater depth played no apparent role in determining the richness in glide habitats, but we do see a relationship between water depth and the cobble sizes. With increased depth we found greater mean b-axis length. This increased axis length then met with increased richness/abundance measurements are discussed previously. This may suggest that with increased depth we see flow increase; as the channel flow strength increases, we have a higher likelihood for woody debris and large particles to be more easily transported downstream.
Uniform distribution of BMIs among the cobble and substrate at these locations indicate a possible preference to choosing glides over riffle habitats, maybe pointing to flow rate being too strong for substrate attachment or the water temperatures being slightly colder and deeper, as well as larger cobble sizes propagating within these regions (Polis 1997). The data collected at every site shows a stronger relationship between abundance and richness and them having more to do with the size of the cobbles themselves. Analysis of the cobbles looked underneath and around support the idea that benthic macro invertebrates prefer to habitate in areas with more surface area of rock, as well as more covered stream bed surface; the larger the cobbles, the larger the area of sandy substrate underneath for which to be protected from the flow rate (Nakano 2001).
The implications of this study include possible linkages between how park management and municipal districts modify stream sections for recreational use and how it can directly affect BMI abundance around and downstream from disturbed sites. Removal of cobble from active streambeds might also prove detrimental to the aquatic communities in and downstream from those sections, as habitable niches would essentially be limited to smaller particle sizes, limiting the number of invertebrates that can inhabit them (Fausch, 2002). Watershed communities should therefore be allowed to thrive with minimal disturbance, as even the alteration of cobbles within a small stretch of stream can have a direct correlation to how these active communities cooperate. References1. Fausch, K.
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(2001). Reciprocal subsidies: dynamic interdependence between terrestrial and aquatic food webs. Proceedings of the National Academy of Sciences, 98(1), 166-170.5. Polis, G.
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D. (1997). Toward an integration of landscape and food web ecology: the dynamics of spatially subsidized food webs. Annual review of ecology and systematics, 28(1), 289-316.Table 8: Tuolomne River, Waterford Site Raw DatasetCobble # Riffle/ Glide (R,G) B-axis (mm) Algae Cover (%) Water Depth (cm) Total Abundance BMI Taxa Richness1 G 82 15 11 11 32 R 94 40 16.3 5 33 G 82 0 14.9 2 24 R 72 0 10.1 10 45 G 78 0 32.2 3 56 R 77 0 11 6 47 R 72 0 10.7 5 48 G 89 0 3.3 0 01 G 70 0 18 13 32 G 80 0 22 3 23 R 80 0 16 5 24 R 70 95 15 21 25 R 50 0 17 3 16 G 70 50 5 0 07 R 70 0 10 2 28 R 110 0 17 5 31 R 70 85 9 10 22 G 85 40 8 16 73 G 100 60 7.5 21 64 R 95 55 8 22 71 R 90 15 14 10 32 G 65 25 15 9 33 R 110 45 30 7 24 G 84 15 30 5 15 R 74 65 25 5 46 R 108 75 14.6 33 31 R 73 65 8 19 62 G 87 0 8.9 12 23 R 89 95 12 38 114 G 104 0 16 10 75 R 99 0 14 15 36 R 87 0 8.5 6 41 R 54 75 20 18 52 R 75 0 10.5 19 53 R 97 15 5 18 34 R 92 50 7.5 18 45 G 105 0 21 17 46 G 79 0 33 14 57 G 82 2 32 14 48 G 76 2 38 14 51 G 70 0 18 13 32 G 80 0 22 3 23 R 80 0 16 5 24 R 70 95 15 21 25 R 50 0 17 3 16 G 70 50 5 0 07 R 70 0 10 2 28 R 110 0 17 5 3