PMFJI, but as a scientist who has both created and consulted
(informally) on designing biological sampling/monitoring databases, may
I offer a suggestion or two?

LAF, it's difficult to grasp your db design from the descriptions you've
posted here. There is clearly some kind of normalization problem that's
preventing you from utilizing the full capabilities of a relational
database. Were I you, I would consider stepping back and reexamining
your entities (real-life persons, places, things, or events that your db
will keep track of) and their attributes (categories of related
information relevent to each entity). Entities & attributes = tables &
fields.

In my experience, managing data from any field survey of a population or
community of organisms will require at least the following entities &
attributes:

Stations - the sampling sites where data are collected. Fields may
include SiteID, SiteName, Latitude, Longitude, County, State, Ecoregion,
and so on.

Events - actual visits (of which there may be one OR MORE) to sites to
collect raw data. Fields may include EventID, SiteID, SampleDate,
SampleTime, ReplicateNum, SampleType, GearUsed (or GearCode), etc.. A
note on SampleType...some developers might argue that it is "easier" to
break up their events tables to reflect the categories of data being
collected (e.g. Benthic, WaterQuality, Habitat). But strictly speaking
this isn't in keeping with the Normal forms.

Organisms - which critters (of which there may be one OR MORE collected
for each unique combination of site+date+time+rep) were collected at
each site for each sampling event , and the number of each. Fields may
include EventID, Taxon (or Taxon ID if you have a taxonomic lookup table
with LatinNames, Taxon level, etc.), and TotalIndividuals.

Organism Details - necessary if you are recording multiple
characteristics or measurements for individual critters. For example:
at Stream X I collected 2 sunfish, 3 bass, and one pickerel. Each fish
was measured for total length, body weight, and whether or not there
were any visible lesions or other anomalies. Fields for the table in
this example may include EventID, TaxonID, FishNum, ParameterMeasured
(or ParameterID if you have a lookup table of standard measurement
parameters and their descriptions), and ParameterValue. You would
probably substitute BandNumber for FishNum to identify individual birds.
You might also want to include a Memo field for comments.

Once your data are organized in a framework that Access understands,
queries become much, much easier. You can calculate the taxonomic
richness at a site for a particular visit, or get a list of all taxa
collected at a site over multiple visits, or generate a list of all
sites where Black-and-White Warblers were collected, or calculate the
proportion of Parula warbler individuals to total abundance of all
individuals at sights visited in Spring, and so on and so on.

Just my $0.02 worth...

Good luck!

LeAnne

LeAnne