Soil Horizons, Water Ecosystems, and Environmental Management: Key Concepts for Biology and Ecology

Soil Horizon Order

The correct vertical sequence from surface to bedrock is O A E B C R

O Horizon

The surface organic layer consisting of leaf litter and decomposed plant matter

A Horizon

Topsoil or the mineral layer darkened by organic matter with the highest biological activity

E Horizon

The eluviated or leached layer that is light in color because minerals have been washed out

B Horizon

The subsoil or illuviated layer where clays and minerals from upper horizons accumulate

C Horizon

The parent material or weathered rock little affected by soil forming processes

R Horizon

The unweathered solid bedrock layer at the base

Non Point Source Pollution

Pollution from diffuse sources like agricultural runoff or street litter rather than a single pipe

Best Management Practices

Methods like rain gardens or riparian buffers designed to reduce runoff

Lotic system

An ecosystem with flowing water such as a creek or river

Lentic system

A still water ecosystem such as a pond or lake

Benthic Macroinvertebrates

Organisms without backbones living on the bottom that serve as long term water quality indicators

Watershed

The total land area that drains into a specific body of water like the Susquehanna or Delaware basins

2026 Bird Calls

Required identification for this year includes the Mourning Dove Chickadee Bald Eagle Chimney Swift Tree Swallow White breasted Nuthatch Osprey and Bufflehead

2026 Mammal Focus

Key species for study this year include the White tailed Deer Squirrels Weasels Mink Fisher River Otter Woodchuck and Opossum

Dendrology

The scientific study and identification of trees and woody plants

Succession

The natural process of change in an ecosystem over time from field to climax forest

Silviculture

The management of forest growth and quality

Biltmore Stick

A specialized tool used to measure tree diameter at breast height and marketable height to estimate board foot volume

DBH

Diameter at Breast Height which is measured at 4.5 feet above the ground on the uphill side of the tree

Clinometer

An instrument used to measure the height of a tree or the percentage of a slope

MBF

One thousand board feet which is a standard unit of measure for timber volume

Basal Area

The cross sectional area of a tree trunk at breast height used to determine forest density

Munsell Soil Color Chart

A standardized book used to identify soil color based on hue value and chroma

2026 Threatened PA Herptiles

Species like the Bog Turtle and Eastern Cricket Frog which have specific habitat requirements in PA

Turbidity

A measure of water clarity based on how much light is scattered by suspended particles

Secchi Disk

A black and white circular disk used to measure the transparency of water

2026 Invasive Plants

Targeted species for this year include Mile a minute weed Japanese Stiltgrass and Tree of Heaven

Biotic Index

A scale used to determine ecosystem health based on the presence of sensitive organisms

Stream Order

A classification system where a first order stream has no tributaries

Ribbon Test

A field method used to determine soil texture by feeling how long of a strip can be formed with wet soil

Mottling

Spots of different colors in the soil that indicate a fluctuating water table and poor drainage

Hydrograph

A graph showing the rate of flow versus time past a specific point in a river

CWD

Chronic Wasting Disease is a fatal neurological disease in deer and elk caused by prions

Carrying Capacity

The maximum population size of a species that an environment can sustain indefinitely

Keystone Species

A species on which other species in an ecosystem largely depend such as the Beaver in aquatic systems

Photic Zone

The upper layer of a body of water where there is enough light for photosynthesis

Epilimnion

The warm upper layer of a stratified lake

Hypolimnion

The cold bottom layer of a stratified lake

Recharge Area

An area where water filters into the ground and reaches the water table resupplying an aquifer

Combined Sewer Overflow

A system where rainwater and domestic sewage are collected in the same pipe which can overflow during heavy rain

Riparian Zone

The interface between land and a river often characterized by unique water loving vegetation

Ecosystem Services

The benefits humans provide from the natural environment such as clean water and pollination

Topographic Map

A map that represents the three dimensional surface of the earth using contour lines

Land Capability Class

A system used to show the suitability of soils for most kinds of field crops ranging from Class 1 to Class 8