Dear Steve,

dispersal distant can be even for larvae, do not forget water birds and some other semi-aquatic vertebrates. But this, I agree, needs much longer period. As to Ephemeroptera you know that they are not feeding in imago state and only reproduction is the main idea of their appearance. But they prefer pacific weather not being active flyers. So, they are staying at place of hatching preferably and can be mooved couple hundred meters by wind. Moreover males, you know are dying after copulation. Females can leave normally 1-2 days and follow males.

With Trichoptera such possibility really exist (mainly not feeding as well but better flyers), as they can live 2-3 weeks, and it is proved for them ability to evaluate the gravitational angle (Jander, 1957; Frisch, Lindauer, 1963)  but anyway dissemination of larvae are preferable, as it can stick by their building silk thred  into legs of water birds. Moreover the larvae of trich. are very resistant against bad env. and can change even their type of metabolism if necessary, and can survey some desiccation.

But even in problematic case with your stream exist possibility for invasion from secondary streams and springs, from not far wells and temporary basins.

As to Reference about dissemination velocity and disp. distance will try to find smthng but have no in my lib. and it isn't small.

Andrey

From my experience in Oregon, among other states, order 3 streams and larger are likely to be perennial, and less frequent order 2 are perennial.  The blue line streams on USGS topographic maps are typically order 4 or 5, and lack the detail of the full stream network.  I am not familiar with Chelan River and its tributaries that contribut to lower sections.  Data from recovery after insecticide - oil spill showed rapid recovery of some tolerant insect forms, slower recovery of others (intolerants) like EPT.  The dam withdrawals would have affected the main stem populations, but would not have affected the tributaries as mentioned by Dr Kovalchuk.  

My coauthored report from 1984 tells of the Willow Creek spill where all or most organisms were killed in significant reach above Heppner, Oregon dam.  Unfortunately I moved, so the short term monitoring did not continue to see colonization of the full diversity of EPT, but we sampled enough streams to know that there was also some natural drift downsteam of insects as well as in response to periods of stress, but do not know how far insects might drift per incident.  

But your concern seems appropriate, as little recovery in 8 years seems excessive duration.  Perhaps changes in the water temperatures, water quality or the clean water releases below the dam for so long have altered and coarsened the substrates to reduce habitat for full diversity assemblage.  The aquatic species present may have shifted toward increased predatory pressure toward EPT.  And dam releases, abrupt changes in flow and pulses seldom mimic normal hydrographs and frequency of change that the natural systems are familiar with and can respond to.  

I do not have the answer to the dispersion ability question, but if the aim of all this is to restore a "natural" state, even by human means (which seem the case with hydrology) maybe the use of artificial substrates incubated upstream of the dam lake, and repositionned bellow it, may "reload" your EPT community more quickly.

But the problem of dams is that drift will continuously deplete your animals downstream without allowing a natural upstream recolonisation. The question is : is the restored channel long enough to host enough sedentary animals to finish their yearly life cycle without removing them by drift?

Thanks to all for the responses. There does seem to be some misconception regarding the nature of the potential upstream source for colonization. The dam at the upstream end of the restored riverine habitat did not create a reservoir, rather it raised the water level in a very large (55 miles long) lake by 10 - 16 feet. The benthic community upstream of the dam is pretty limited. We will add drift sampling to the Above-Dam effort in 2017. The results below were from grab samples of substrate in the somewhat riverine 1000 meter former river channel that extends from the natural lake outlet downstream to the face of the dam. This inundated section is roughly 3 - 10 meters deep, depending on time of year. The benthic organisms in the grab samples had the following characteristics. The restored river downstream from the dam has similar number of taxa (richness) to the May sample, but more diversity with richness of E, T and clinger of 1-2, 3-5, and 6-9, respectively. Also, percent pollution tolerant is 3% - 10% for sample locations in the restored river and predator percent is 9% - 26%. Thus, there has been colonization by taxa that are not present upstream of the dam. However, P richness remains 0 and I am trying to determine if plecoptera taxa are poor travelers by flight or other dispersal (birds, for example) when there aren't any riverine sources within 15 km radius of the site. Artificial introduction of a broader mix of taxa via plates or cobble baskets from appropriate donor streams would be an interesting experiment and I would appreciate any feedback on where to find literature reporting on benthic organism introductions of this type.

                                                             May                                       August

METRICS

Taxa Richness                                      28                                           14

E Richness                                              0                                            0

P Richness                                              0                                            0

T Richness                                              1                                            0

Pollution Sensitive Richness                   0                                            0

Clinger Richness                                     1                                            0

Semivoltine Richness                              1                                            1

Pollution Tolerant Percent               46.34%                                  45.95%

Predator Percent                               7.32%                                      1.8%

Dominant Taxa (3) Percent             50.00%                                   64.86%

Adult stoneflies and caddisflies are considered to be fairly weak fliers I believe. Given a 9 mile distance to the nearest source population, there may not have been enough time since 2009 for recolonization to have occurred. 

I think it would be worth trying to be more specific about the plecopteran species that might colonise the habitat at your restored location, based on similar streams in the area, then look at their specific dispersal ability. Whilst plecopterans are notoriously poor fliers some are more aerial than others. Many species don't fly at all, strictly speaking. It may be that the natural habitat you have restored may not be suitable for the species that are more dispersive. In the UK we would use the RIVPACS predictive model to predict the likelihood of different species occurring at a site, given the natural environmental characteristics of the site - I'm not sure if you have a similar model but a manual comparison of the fauna of neighbouring sites of similar character would be sufficient. 

It's an interesting situation where the stream section is sandwiched between two lentic waterbodies which hamper small-scale colonisation movements. I don't see why some individuals of species with a reasonable capacity for flight shouldn't be carried in strong winds, although that would be a pretty random process and may take a certain set of circumstances to occur. As has been suggested, if all else fails it would be interesting to try seeding plecoptera from an adjacent site with similar habitat characteristics to see if they manage to establish a population.

Hi Steven, 

You are right that there's a real scarcity of information on dispersal abilities for adult stages of aquatic taxa. Generally speaking, T>E>P however dispersal abilities vary widely within these orders (particularly T and E) adding a layer of complexity to your question. A few good papers to help you put your colonization rates in context might be:

Alp, M., I. Keller, A. M. Westram, and C. T. Robinson. 2012.

How river structure and biological traits influence gene flow:

a population genetic study of two stream invertebrates with

differing dispersal abilities. Freshwater Biology 57:969–981.

Kovats, Z., J. Ciborowski, and L. Corkum. 1996. Inland dispersal

of adult aquatic insects. Freshwater Biology 36:265–276.

Morán-Ordóñez, A., A. Pavlova, A. M. Pinder, L. Sim, P.

Sunnucks, R. M. Thompson, and J. Davis. 2015. Aquatic communities

in arid landscapes: local conditions, dispersal traits

and landscape configuration determine local biodiversity. Diversity

and Distributions. doi:10.1111/ddi.12342

Petersen, I., Z. Masters, A. G. Hildrew, and S. J. Ormerod.

2004. Dispersal of adult aquatic insects in catchments of

differing land use. Journal of Applied Ecology 41:934–950.

Thompson, R., and C. Townsend. 2006. A truce with neutral

theory: local deterministic factors, species traits and dispersal

limitation together determine patterns of diversity in stream

invertebrates. Journal of Animal Ecology 75:476–484.

While my results might only be tangentially relevant to you, I summarized some of these publications in the attached paper which might also help you find more relevant work for your needs. Best of luck.

Matt

Article Spatial scale and dispersal influence metacommunity dynamics...

i agree with Hansen