what would cause sand in a fresh water stream to have a soil pH of 6 (acidic)?

Question

what would be the cause of this acidic reading?

Answer 1

most fresh water is slightly acidic. 6 is not bad. anything lower might but it depends on what you are doing. 7 is the middle. leaves and other organic matter dissolves and makes the water acidic. WATER DISSOLVES EVERYTHING IT COMES IN CONTACT WITH! it is a question of balance.

Answer 2

Primarily tannic acid from rotting leaves. It's acidic in that the pH is lower than 7.0 (neutral pH). But for stream water it is in the "normal" range.

Answer 3

In a lab the concept of acidity VS alkalinity is very precise but in the soil all living things have a range they tolerate. Most plants grow best at a pH of 6.5 as most plant nutrients are available for uptake by the roots at this pH level, the pH range of most soils lies between 5.5 and 7.5.
Slightly acidic soils range form pH 5.8 to 6.5 and extremely acid soils range from pH 4.0-5.0. This definition is based on how the pH effects the nutrient availability. The greatest diversity are happy with pH 6 - 7
N (nitrogen) – readily available from pH 6 to 8 but if pH <6 nitrifying bacteria are unable to live. A pH level of around 6.3-6.8 is the optimum range preferred by most soil bacteria, although fungi, molds, and anaerobic bacteria have a broader tolerance and tend to multiply at lower pH values.
P (phosphate)– availability reduced at a lower pH<5.5 as it binds with Al and Fe. P is most available at pH 6-7. Basic soil conditions (pH > 7.5) cause excessive calcium to be present in soil solution, which can precipitate with P decreasing P availability.
K (potassium) – most available at pH 5.5-7

Acidity or alkalinity of the soil is determined by the mineral content. The presence of calcium ions (Ca++) is usually what determines the pH of soil, as they displace hydrogen ions in solution. A soil particle with a full amount of H+ ions is weakly acid, but the presence of calcium ions makes it neutral or alkaline. Calcium is leached away so soils have a tendency to become acid and this occurs faster in sandy soils.
Soil types contain different ratios of minerals. Soils developed from basic rocks generally have higher pH values than those formed from acid rocks.